{"id":9453,"date":"2026-09-15T09:00:00","date_gmt":"2026-09-15T09:00:00","guid":{"rendered":"https:\/\/www.simplywise.com\/blog\/?p=9453"},"modified":"2026-09-15T15:38:05","modified_gmt":"2026-09-15T15:38:05","slug":"insulation-calculator","status":"publish","type":"post","link":"https:\/\/www.simplywise.com\/blog\/insulation-calculator\/","title":{"rendered":"Insulation Calculator"},"content":{"rendered":"<p><script>\ndocument.addEventListener('DOMContentLoaded', function() {\n  var sels = ['.entry-header','.page-header','article > h1:first-child','.entry-footer'];\n  sels.forEach(function(s){document.querySelectorAll(s).forEach(function(el){el.style.display='none';});});\n  var el = document.querySelector('.sw-a');\n  while (el && el !== document.body) {\n    el.style.maxWidth='100%'; el.style.width='100%'; el.style.padding='0'; el.style.margin='0';\n    el.style.float='none'; el.style.flex='0 0 100%';\n    el = el.parentElement;\n  }\n  document.body.style.marginTop='0'; 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14px;border-radius:16px;}.swc__grid{gap:10px;}.swc__num{font-size:38px;}.swc__preset{padding:12px 0;}.swc__presets{flex-wrap:wrap;}.swc__custom{flex:1 1 100%;}}<\/style>\n<p><script>\n(function(){\n  try{\n    var b=document.body;\n    if(b && b.classList){b.classList.add('single-post');}\n  }catch(e){}\n})();\n<\/script><\/p>\n<article class=\"pm\">\n<header class=\"pm__hero\">\n<div class=\"pm__inner\">\n<nav class=\"pm__crumb\">Blog &nbsp;&rsaquo;&nbsp; How to Estimate<\/nav>\n<p><span class=\"pm__eyebrow\">Contractor Calculator &middot; Insulation<\/span><\/p>\n<h1>Insulation Calculator: Bags, Batts, and R-Value by Zone<\/h1>\n<p class=\"pm__dek\">Set the area, cavity depth, framing spacing, and target R-value. Bag counts, bundle counts, and the climate zone check update as you type.<\/p>\n<p class=\"pm__dek-cta\">Pricing the whole job? <a href=\"https:\/\/swcostestimator.app.link\/ce-ai\" rel=\"noopener\" target=\"_blank\">Estimate it from a photo<\/a> in about six seconds.<\/p>\n<div class=\"pm__rating\"><span class=\"pm__stars\">&#9733;&#9733;&#9733;&#9733;&#9733;<\/span> <b>4.8<\/b> <span class=\"pm__rating-sub\">on the App Store<\/span><\/div>\n<div class=\"pm__meta\">\n<span>SimplyWise<\/span><br \/>\n<i><\/i><br \/>\n<span>Updated September 15, 2026<\/span><br \/>\n<i><\/i><br \/>\n<span>5 min read<\/span>\n<\/div>\n<div class=\"swc\" id=\"swcalc\">\n<span class=\"swc__kicker\">Free Insulation Calculator<\/span><\/p>\n<div class=\"swc__title\">Size the bags, bundles, or foam for your R-value<\/div>\n<div class=\"swc__field\"><label for=\"swc-area\">Insulation type<\/label><\/p>\n<div class=\"swc__presets\" id=\"swc-type\"><button type=\"button\" class=\"swc__preset\" data-k=\"batt\">Batts<\/button><button type=\"button\" class=\"swc__preset is-on\" data-k=\"fill\">Blown fill<\/button><button type=\"button\" class=\"swc__preset\" data-k=\"foam\">Spray foam<\/button><\/div>\n<\/div>\n<div class=\"swc__grid\">\n<div class=\"swc__field\"><label for=\"swc-area\">Attic or wall area (sq ft)<\/label><input id=\"swc-area\" type=\"number\" inputmode=\"decimal\" min=\"1\" max=\"100000\" step=\"10\" value=\"1200\"><\/div>\n<div class=\"swc__field\"><label for=\"swc-depth\">Cavity depth (in)<\/label><input id=\"swc-depth\" type=\"number\" inputmode=\"decimal\" min=\"0.5\" max=\"40\" step=\"0.25\" value=\"10.5\"><\/div>\n<\/div>\n<div class=\"swc__field\"><label for=\"swc-area\">Framing spacing<\/label><\/p>\n<div class=\"swc__presets\" id=\"swc-space\"><button type=\"button\" class=\"swc__preset\" data-s=\"16\">16 in on center<\/button><button type=\"button\" class=\"swc__preset is-on\" data-s=\"24\">24 in on center<\/button><\/div>\n<p><span class=\"swc__hint\">Sets the batt width. Blown fill and foam ignore it.<\/span><\/div>\n<div class=\"swc__field\"><label for=\"swc-area\">Target R-value<\/label><\/p>\n<div class=\"swc__presets\" id=\"swc-rval\"><button type=\"button\" class=\"swc__preset\" data-r=\"13\">R-13<\/button><button type=\"button\" class=\"swc__preset\" data-r=\"19\">R-19<\/button><button type=\"button\" class=\"swc__preset is-on\" data-r=\"30\">R-30<\/button><button type=\"button\" class=\"swc__preset\" data-r=\"38\">R-38<\/button><button type=\"button\" class=\"swc__preset\" data-r=\"49\">R-49<\/button><button type=\"button\" class=\"swc__preset\" data-r=\"60\">R-60<\/button><\/div>\n<\/div>\n<div class=\"swc__out\" aria-live=\"polite\">\n<div class=\"swc__big\"><span class=\"swc__num\" id=\"swc-units\">15 to 17<\/span><span class=\"swc__unit\" id=\"swc-unitlabel\">bags to order<\/span><\/div>\n<div class=\"swc__row\"><span>Coverage per unit<\/span><b id=\"swc-cov\">73 to 81 sq ft per bag<\/b><\/div>\n<div class=\"swc__row\"><span>Depth at this R-value<\/span><b id=\"swc-depthout\">10.5 to 10.8 in<\/b><\/div>\n<div class=\"swc__row\"><span>R-value your cavity holds<\/span><b id=\"swc-ach\">R-30<\/b><\/div>\n<div class=\"swc__row swc__row--cost\"><span>Climate zone check<\/span><b id=\"swc-zone\">Meets the zone 1 attic target<\/b><\/div>\n<p class=\"swc__note\" id=\"swc-note\">Coverage spans the Owens Corning and Johns Manville attic charts. Charts and zone targets read September 11, 2026.<\/p>\n<\/div>\n<\/div>\n<p><script>\n(function(){\n  \/\/ SOURCED DATA, one block, swap ready. Every figure was read 2026-09-11.\n  \/\/ FILL_OC: Owens Corning, ProCat Professional Loosefill Insulation,\n  \/\/   \"Specifications for Open Blow Attics\", Pub. No. 10021711-A, March 2026.\n  \/\/   [maximum net coverage sq ft per bag, minimum initial installed thickness in].\n  \/\/ FILL_JM: Johns Manville, Climate Pro B7600 Fiberglass Blowing Wool\n  \/\/   Insulation, Attic Coverage card. [maximum net coverage sq ft per bag,\n  \/\/   minimum installed thickness in].\n  \/\/ BATT16 \/ BATT24 \/ BATT_T: Johns Manville Fiberglass Manufacturers Fact\n  \/\/   Sheet, Kraft Faced Thermal and Acoustical Batts. Sq ft per bag by item\n  \/\/   number: 15 or 16 in wide for 16 in on center, 23 or 24 in wide for 24 in\n  \/\/   on center. R-13 K1241 and K292, R-19 K1250 and K1251, R-30 K1242 and\n  \/\/   K1243, R-38 K1244 and K1245, R-49 K4916 and K4924. No kraft batt at R-60.\n  \/\/ FOAM_R: JM Corbond III Closed Cell Spray Polyurethane Foam data sheet,\n  \/\/   R-value per inch 7.0 by ASTM C518 aged.\n  \/\/ ZONE targets: 2021 IECC attic levels as published by ENERGY STAR,\n  \/\/   Recommended Home Insulation R-Values, matching IRC N1102.1.3 and IECC\n  \/\/   Table R402.1.3 (zone 1 R-30, zones 2 and 3 R-49, zones 4 through 8 R-60).\n  var FILL_OC={13:[198.0,4.75],19:[128.7,7.00],30:[80.6,10.50],38:[60.9,13.25],49:[46.4,16.50],60:[36.9,19.75]};\n  var FILL_JM={13:[176,4.9],19:[119,7.0],30:[73,10.8],38:[57,13.4],49:[43,16.9],60:[34,20.2]};\n  var BATT16={13:106.56,19:87.18,30:58.66,38:42.66,49:32.00};\n  var BATT24={13:163.39,19:133.68,30:88.00,38:64.00,49:48.00};\n  var BATT_T={13:3.50,19:6.50,30:10.25,38:12.50,49:13.50};\n  var FOAM_R=7.0;\n  var FILL_LADDER=[[4.75,13],[5.25,14],[5.50,15],[5.75,16],[6.25,17],[6.50,18],[7.00,19],[7.25,20],[7.50,21],[8.00,22],[8.25,23],[8.50,24],[9.00,25],[9.25,26],[9.50,27],[10.00,28],[10.25,29],[10.50,30],[11.00,31],[11.25,32],[11.50,33],[11.75,34],[12.25,35],[12.50,36],[12.75,37],[13.25,38],[13.50,39],[13.75,40],[14.00,41],[14.50,42],[14.75,43],[15.00,44],[15.25,45],[15.75,46],[16.00,47],[16.25,48],[16.50,49],[16.75,50],[17.25,51],[17.50,52],[17.75,53],[18.00,54],[18.25,55],[18.75,56],[19.00,57],[19.25,58],[19.50,59],[19.75,60]];\n  var BATT_LADDER=[[3.50,15],[5.50,21],[6.50,19],[8.25,25],[10.25,30],[12.00,38],[12.50,38],[13.50,49]];\n  var DATED=' Charts and zone targets read September 11, 2026.';\n  var NOTE_FILL='Coverage spans the Owens Corning and Johns Manville attic charts.'+DATED;\n  var NOTE_BATT='Bundle coverage is the Johns Manville kraft faced batt chart at this spacing.'+DATED;\n  var NOTE_BATT60='Johns Manville publishes no kraft faced batt at R-60. Stack a second layer over R-49, or blow loose fill.'+DATED;\n  var NOTE_FOAM='Closed cell foam at R-7.0 per inch, JM Corbond III data sheet.'+DATED;\n  var kind='fill', space=24, rv=30;\n  function $(i){return document.getElementById(i);}\n  function ceil6(x){return Math.ceil(Number(x.toFixed(6)));}\n  function floor6(x){return Math.floor(Number(x.toFixed(6)));}\n  function val(el,lo,hi){var v=parseFloat(el.value);if(!isFinite(v)||v<lo||v>hi){return null;}return v;}\n  function rng(a,b,dp){var lo=Math.min(a,b).toFixed(dp),hi=Math.max(a,b).toFixed(dp);return (lo===hi)?lo:(lo+' to '+hi);}\n  function ladder(tbl,d){var best=null;for(var i=0;i<tbl.length;i++){if(d>=tbl[i][0]&&(best===null||tbl[i][1]>best)){best=tbl[i][1];}}return best;}\n  function zoneText(r){\n    if(r<30){return 'Short of every zone. Zone 1 wants R-30';}\n    if(r<49){return 'Meets the zone 1 attic target';}\n    if(r<60){return 'Meets zones 1 through 3. Zones 4 to 8 want R-60';}\n    return 'Meets the attic target in all eight zones';\n  }\n  function neutral(){\n    $('swc-units').textContent='0';\n    $('swc-cov').textContent='enter area and depth';\n    $('swc-depthout').textContent='0 in';\n    $('swc-ach').textContent='R-0';\n    $('swc-zone').textContent='Enter area and depth to check the zone target';\n    $('swc-note').textContent=NOTE_FILL;\n  }\n  function run(){\n    var area=val($('swc-area'),1,100000), depth=val($('swc-depth'),0.5,40);\n    if(area===null||depth===null){neutral();return;}\n    var units, unitlabel, cov, dep, ach, note;\n    if(kind==='fill'){\n      var oc=FILL_OC[rv], jm=FILL_JM[rv];\n      var lo=ceil6(area\/Math.max(oc[0],jm[0])), hi=ceil6(area\/Math.min(oc[0],jm[0]));\n      units=(lo===hi)?String(lo):(lo+' to '+hi);\n      unitlabel='bags to order';\n      cov=rng(oc[0],jm[0],0)+' sq ft per bag';\n      dep=rng(oc[1],jm[1],1)+' in';\n      ach=ladder(FILL_LADDER,depth);\n      note=NOTE_FILL;\n    }else if(kind==='batt'){\n      var tbl=(space===16)?BATT16:BATT24, c=tbl[rv];\n      ach=ladder(BATT_LADDER,depth);\n      unitlabel='bundles to order';\n      if(!c){\n        units='0'; cov='no kraft batt at R-'+rv; dep='not published'; note=NOTE_BATT60;\n      }else{\n        units=String(ceil6(area\/c)); cov=c.toFixed(2)+' sq ft per bundle';\n        dep=BATT_T[rv].toFixed(2)+' in'; note=NOTE_BATT;\n      }\n    }else{\n      units=ceil6(area*depth).toLocaleString('en-US');\n      unitlabel='board feet to order';\n      cov='R-7.0 per inch, closed cell';\n      dep=(Math.ceil(Number((rv\/FOAM_R*10).toFixed(6)))\/10).toFixed(1)+' in';\n      ach=floor6(depth*FOAM_R);\n      note=NOTE_FOAM;\n    }\n    $('swc-units').textContent=units;\n    $('swc-unitlabel').textContent=unitlabel;\n    $('swc-cov').textContent=cov;\n    $('swc-depthout').textContent=dep;\n    $('swc-ach').textContent=(ach===null)?'cavity too shallow':('R-'+ach);\n    $('swc-zone').textContent=(ach===null)?'Cavity too shallow for any zone target':zoneText(ach);\n    $('swc-note').textContent=note;\n  }\n  function wire(id,attr,setter){\n    var bs=document.querySelectorAll('#'+id+' .swc__preset');\n    bs.forEach(function(b){b.addEventListener('click',function(){\n      setter(b.getAttribute(attr));\n      bs.forEach(function(x){x.classList.remove('is-on');});\n      b.classList.add('is-on');\n      run();\n    });});\n  }\n  wire('swc-type','data-k',function(v){kind=v;});\n  wire('swc-space','data-s',function(v){space=parseInt(v,10);});\n  wire('swc-rval','data-r',function(v){rv=parseInt(v,10);});\n  ['swc-area','swc-depth'].forEach(function(i){$(i).addEventListener('input',run);});\n  run();\n})();\n<\/script><\/p>\n<figure class=\"pm__fig\">\n<img decoding=\"async\" alt=\"Attic space with insulation laid between the joists under a framed roof\" loading=\"eager\" src=\"https:\/\/images.unsplash.com\/photo-1752852381113-7d93abc9d7ea?w=1400&amp;h=700&amp;fit=crop&amp;q=80&amp;auto=format\"\/><br \/>\n<\/figure>\n<\/div>\n<\/header>\n<div class=\"pm__body\">\n<div class=\"pm__inner\">\n<aside class=\"pm__tldr\">\n<div class=\"pm__tldr-label\">At a glance<\/div>\n<ol>\n<li>Bags equal area divided by the coverage the maker prints at your R-value.<\/li>\n<li>At R-30 Owens Corning covers 80.6 sq ft a bag and Johns Manville covers 73.<\/li>\n<li>Batt bundles change with spacing. R-30 covers 58.66 sq ft at 16 in on center, 88 at 24 in.<\/li>\n<li>Closed cell foam runs R-7.0 an inch, so a 3.5 in cavity tops out near R-24. The JM sheet rounds that to 25. We round down.<\/li>\n<li>The 2021 code wants R-60 in the attic across zones 4 through 8.<\/li>\n<li>Bags and bundles round up.<\/li>\n<\/ol>\n<div class=\"pm__tldr-cta\"><span>Turn the material count into a priced, branded quote. Free to try.<\/span><a href=\"https:\/\/swcostestimator.app.link\/ce-ai\" rel=\"noopener\" target=\"_blank\">SimplyWise Cost Estimator<\/a><\/div>\n<\/aside>\n<h2>How the insulation calculator works<\/h2>\n<p>Insulation is not counted by volume. It is counted by how much area one bag or bundle covers at your R-value, and the maker prints that on the bag.<\/p>\n<p>So the math is a division. Area divided by coverage at the target R-value, rounded up. Chase a higher R and coverage per bag drops, because the same material goes down deeper.<\/p>\n<p>Cavity depth is the other half. The chart sets a settled thickness for each R-value, and if the depth is short the R-value is short, whatever the label says.<\/p>\n<h2>Worked example: R-30 across a 1,200 sq ft attic<\/h2>\n<p>At R-30 the Owens Corning open blow chart allows one bag to cover no more than <strong>80.6 sq ft<\/strong>. Divide 1,200 by 80.6 and you get 14.89, which rounds up to <strong>15 bags<\/strong>.<\/p>\n<p>Run the same attic on the Johns Manville chart and R-30 covers 73 sq ft a bag, so 1,200 becomes 16.44, or <strong>17 bags<\/strong>. Two honest charts, two bag counts.<\/p>\n<p>Both charts also set a depth. R-30 needs 10.5 in of settled fill on the Owens Corning card and 10.8 in on the Johns Manville card. Blow it at 8 in and you sold R-30 and installed about R-22.<\/p>\n<p class=\"pm__inline-cta\"><a href=\"https:\/\/swcostestimator.app.link\/ce-ai\" rel=\"noopener\" target=\"_blank\">SimplyWise Cost Estimator<\/a> turns a photo of the space into an itemized estimate in about 6 seconds.<\/p>\n<h2>Blown fill coverage per bag by R-value<\/h2>\n<p>Maximum net coverage in square feet per bag, and settled depth in inches, off the two maker charts.<\/p>\n<table class=\"pm__table\">\n<thead>\n<tr>\n<th>R-value<\/th>\n<th>Owens Corning<\/th>\n<th>Johns Manville<\/th>\n<th>Settled depth<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>R-13<\/td>\n<td>198.0<\/td>\n<td>176<\/td>\n<td>4.8 to 4.9<\/td>\n<\/tr>\n<tr>\n<td>R-19<\/td>\n<td>128.7<\/td>\n<td>119<\/td>\n<td>7.0<\/td>\n<\/tr>\n<tr>\n<td>R-30<\/td>\n<td>80.6<\/td>\n<td>73<\/td>\n<td>10.5 to 10.8<\/td>\n<\/tr>\n<tr>\n<td>R-38<\/td>\n<td>60.9<\/td>\n<td>57<\/td>\n<td>13.3 to 13.4<\/td>\n<\/tr>\n<tr>\n<td>R-49<\/td>\n<td>46.4<\/td>\n<td>43<\/td>\n<td>16.5 to 16.9<\/td>\n<\/tr>\n<tr>\n<td>R-60<\/td>\n<td>36.9<\/td>\n<td>34<\/td>\n<td>19.8 to 20.2<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<section class=\"pm__promo\">\n<h2>Turn the count into insulation cost per square foot<\/h2>\n<p>SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds. Pricing is $29.99\/mo or $239.99\/yr, about $20\/mo on annual, with a 7-day free trial.<\/p>\n<p><a class=\"pm__btn\" href=\"https:\/\/swcostestimator.app.link\/ce-ai\" rel=\"noopener\" target=\"_blank\">SimplyWise Cost Estimator<\/a><br \/>\n<\/section>\n<h2>Batt bundle coverage by framing spacing<\/h2>\n<p>A 15 or 16 in batt fits 16 in on center and a 23 or 24 in batt fits 24 in, so the wider bundle covers more floor for the same piece count. Coverage is square feet per bundle, thickness in inches.<\/p>\n<table class=\"pm__table\">\n<thead>\n<tr>\n<th>R-value<\/th>\n<th>16 in on center<\/th>\n<th>24 in on center<\/th>\n<th>Thickness<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>R-13<\/td>\n<td>106.56<\/td>\n<td>163.39<\/td>\n<td>3.50<\/td>\n<\/tr>\n<tr>\n<td>R-19<\/td>\n<td>87.18<\/td>\n<td>133.68<\/td>\n<td>6.50<\/td>\n<\/tr>\n<tr>\n<td>R-30<\/td>\n<td>58.66<\/td>\n<td>88.00<\/td>\n<td>10.25<\/td>\n<\/tr>\n<tr>\n<td>R-38<\/td>\n<td>42.66<\/td>\n<td>64.00<\/td>\n<td>12.50<\/td>\n<\/tr>\n<tr>\n<td>R-49<\/td>\n<td>32.00<\/td>\n<td>48.00<\/td>\n<td>13.50<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>No kraft faced batt reaches R-60, which is why deep attics go to loose fill or a second layer over R-49.<\/p>\n<h2>What your climate zone asks for<\/h2>\n<p>The 2021 energy code raised attic levels hard. Zones 4 through 8 moved from R-49 to R-60, and zones 2 and 3 moved from R-38 to R-49. Zone 1 sits at R-30.<\/p>\n<p>In blown fill that is 10.5 to 10.8 in of settled depth for zone 1, 16.5 to 16.9 in for zones 2 and 3, and 19.8 to 20.2 in for zones 4 and up. A 2x10 bay holds about 9.25 in, so R-60 buries the joists.<\/p>\n<h2>Order the count you will install<\/h2>\n<ol class=\"pm__steps\">\n<li>\n<h3>Measure net area, not gross<\/h3>\n<p>Subtract what stays open, such as a chase or a stair well. Charts are written against net square footage.<\/p>\n<\/li>\n<li>\n<h3>Pick the R-value first, then the material<\/h3>\n<p>The target sets the coverage. Picking the bag first is how crews end up two bags short at four in the afternoon.<\/p>\n<\/li>\n<li>\n<h3>Check the depth before you quote<\/h3>\n<p>Compare the settled thickness for your target against the cavity you have. If the cavity is shallower, either the assembly changes or the R-value does.<\/p>\n<\/li>\n<li>\n<h3>Round up, every time<\/h3>\n<p>Bags and bundles are whole units. Round up, then add for the piece cut wrong.<\/p>\n<\/li>\n<\/ol>\n<div class=\"pm__next\">\n<h2>Keep reading<\/h2>\n<ul>\n<li><a href=\"https:\/\/www.simplywise.com\/blog\/construction-calculators\/\">Construction Calculators Hub<\/a><\/li>\n<li><a href=\"https:\/\/www.simplywise.com\/blog\/drywall-sheet-and-mud-calculator\/\">Drywall Calculator: Sheets and Mud<\/a><\/li>\n<li><a href=\"https:\/\/www.simplywise.com\/blog\/drywall-installation-cost\/\">Drywall Installation Cost<\/a><\/li>\n<li><a href=\"https:\/\/www.simplywise.com\/blog\/roof-replacement-cost\/\">Roof Replacement Cost<\/a><\/li>\n<\/ul>\n<\/div>\n<div class=\"pm__sources\">\n<h2>Sources<\/h2>\n<h3>Maker coverage charts<\/h3>\n<ul>\n<li><a href=\"https:\/\/dcpd6wotaa0mb.cloudfront.net\/mdms\/dms\/Residential%20Insulation\/10021711\/10021711-ProCat-Professional-Loosefill-Coverage-Chart-Spec-Card.pdf\" rel=\"noopener\" target=\"_blank\">Owens Corning, ProCat Professional Loosefill Insulation, Specifications for Open Blow Attics<\/a> (Pub. No. 10021711-A, March 2026; verified 2026-09-11).<\/li>\n<li><a href=\"https:\/\/www.jm.com\/content\/dam\/jm\/global\/en\/building-insulation\/Files\/BI%20Toolbox\/B7600-Climate-Pro-Attic-Card.pdf\" rel=\"noopener\" target=\"_blank\">Johns Manville, Climate Pro B7600 Fiberglass Blowing Wool, Attic Coverage<\/a> (coverage per bag and installed thickness; verified 2026-09-11).<\/li>\n<li><a href=\"https:\/\/www.jm.com\/content\/dam\/jm\/global\/en\/building-insulation\/Files\/BI%20Toolbox\/JM%20Fiberglass%20Manufacturers%20Fact%20Sheet.pdf\" rel=\"noopener\" target=\"_blank\">Johns Manville, Fiberglass Manufacturers Fact Sheet<\/a> (kraft faced batt coverage by item number; verified 2026-09-11).<\/li>\n<li><a href=\"https:\/\/www.jm.com\/content\/dam\/jm\/global\/en\/building-insulation\/Files\/BI%20Data%20Sheets\/Resi%20and%20Commercial\/JMCorbondIII-ds.pdf\" rel=\"noopener\" target=\"_blank\">Johns Manville, JM Corbond III Closed Cell Spray Polyurethane Foam data sheet<\/a> (R-7.0 per inch; verified 2026-09-11).<\/li>\n<\/ul>\n<h3>Code and climate zones<\/h3>\n<ul>\n<li><a href=\"https:\/\/www.energystar.gov\/saveathome\/seal_insulate\/identify-problems-you-want-fix\/diy-checks-inspections\/insulation-r-values\" rel=\"noopener\" target=\"_blank\">ENERGY STAR, Recommended Home Insulation R-Values<\/a> (attic targets by zone; verified 2026-09-11).<\/li>\n<li><a href=\"https:\/\/montgomerycountymd.gov\/DPS\/Resources\/Files\/Outreach-Presentations\/2021%20Code%20Changes%20IECC%202%20Final.pdf\" rel=\"noopener\" target=\"_blank\">Montgomery County MD, 2021 Residential Energy Code Changes<\/a> (Table R402.1.3 ceiling values; verified 2026-09-11).<\/li>\n<li><a href=\"https:\/\/www.energycodes.gov\/sites\/default\/files\/2021-07\/2021_IECC_PreliminaryDetermination_TSD.pdf\" rel=\"noopener\" target=\"_blank\">US Department of Energy, 2021 energy code residential analysis<\/a> (Table D.5; verified 2026-09-11).<\/li>\n<li><a href=\"https:\/\/basc.pnnl.gov\/images\/climate-zone-map-iecc-2021\" rel=\"noopener\" target=\"_blank\">PNNL Building America, Climate Zone Map<\/a> (zone boundaries; verified 2026-09-11).<\/li>\n<\/ul>\n<h3>Product<\/h3>\n<ul>\n<li><a href=\"https:\/\/apps.apple.com\/us\/app\/simplywise-cost-estimator\/id6670619664\" rel=\"noopener\" target=\"_blank\">SimplyWise Cost Estimator, App Store<\/a> (4.8 rating; verified 2026-09-09).<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<section class=\"pm__faq\">\n<div class=\"pm__inner\">\n<h2>Common questions about sizing insulation<\/h2>\n<h3>Bags, bundles, and coverage<\/h3>\n<details>\n<summary>How many bags of blown insulation do I need for R-30?<\/summary>\n<div>\n<p>Divide area by the coverage on the bag. At R-30 that is 80.6 sq ft on the Owens Corning chart and 73 on the Johns Manville chart, so 1,200 sq ft takes 15 to 17 bags.<\/p>\n<\/div>\n<\/details>\n<details>\n<summary>How much does one bundle of batts cover?<\/summary>\n<div>\n<p>Kraft faced R-30 covers 58.66 sq ft at 16 in on center and 88.00 sq ft at 24 in.<\/p>\n<\/div>\n<\/details>\n<details>\n<summary>Why do two makers give different bag counts?<\/summary>\n<div>\n<p>Each maker tests its own product and prints its own coverage. The R-value matches, the density does not. Buy off the chart on the bag you are using.<\/p>\n<\/div>\n<\/details>\n<h3>Depth, R-value, and code<\/h3>\n<details>\n<summary>What R-value does my climate zone need in the attic?<\/summary>\n<div>\n<p>Zone 1 wants R-30, zones 2 and 3 want R-49, and zones 4 through 8 want R-60. Walls are set separately.<\/p>\n<\/div>\n<\/details>\n<details>\n<summary>How deep is R-60 in blown fill?<\/summary>\n<div>\n<p>About 19.8 to 20.2 in of settled thickness. That is deeper than any common joist, so the fill covers the framing rather than sitting between it.<\/p>\n<\/div>\n<\/details>\n<details>\n<summary>Can SimplyWise work out insulation cost per square foot from a photo?<\/summary>\n<div>\n<p>Yes. SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds, with material and labor lines. Free to try, at $29.99\/mo.<\/p>\n<\/div>\n<\/details>\n<\/div>\n<\/section>\n<section class=\"pm__final\">\n<div class=\"pm__inner\">\n<span class=\"pm__eyebrow\">Count it once, bid it once<\/span><\/p>\n<h2>Turn the bag count into a signed job.<\/h2>\n<p>Snap a photo and get an itemized estimate in about 6 seconds. Free to try.<\/p>\n<p><a class=\"pm__btn pm__btn--lg\" href=\"https:\/\/swcostestimator.app.link\/ce-ai\" rel=\"noopener\" target=\"_blank\">SimplyWise Cost Estimator<\/a>\n<\/div>\n<\/section>\n<\/article>\n<p><script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"BlogPosting\",\n  \"headline\": \"Insulation Calculator: Bags, Batts, and R-Value by Zone\",\n  \"description\": \"An insulation calculator that turns attic or wall area, cavity depth, framing spacing, and a target R-value into bag counts, batt bundles, board feet, and a climate zone check.\",\n  \"author\": {\n    \"@type\": \"Organization\",\n    \"name\": \"SimplyWise\"\n  },\n  \"publisher\": {\n    \"@type\": \"Organization\",\n    \"name\": \"SimplyWise\",\n    \"logo\": {\n      \"@type\": \"ImageObject\",\n      \"url\": \"https:\/\/www.simplywise.com\/icon-512x512.png\"\n    }\n  },\n  \"datePublished\": \"2026-09-15\",\n  \"dateModified\": \"2026-09-15\",\n  \"mainEntityOfPage\": {\n    \"@type\": \"WebPage\",\n    \"@id\": \"https:\/\/www.simplywise.com\/blog\/insulation-calculator\/\"\n  },\n  \"url\": \"https:\/\/www.simplywise.com\/blog\/insulation-calculator\/\",\n  \"image\": [\n    \"https:\/\/images.unsplash.com\/photo-1752852381113-7d93abc9d7ea?w=1400&h=700&fit=crop&q=80&auto=format\"\n  ]\n}\n<\/script><br \/>\n<script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"HowTo\",\n  \"name\": \"How to Calculate Insulation Bags, Batt Bundles, and R-Value\",\n  \"step\": [\n    {\n      \"@type\": \"HowToStep\",\n      \"position\": 1,\n      \"name\": \"Measure net area, not gross\",\n      \"text\": \"Take the flat area you are covering and subtract what stays open, such as a mechanical chase or a stair opening. Manufacturer coverage charts are written against net square footage.\"\n    },\n    {\n      \"@type\": \"HowToStep\",\n      \"position\": 2,\n      \"name\": \"Pick the R-value first, then the material\",\n      \"text\": \"The target R-value sets the coverage per bag or per bundle on the manufacturer chart, so choose the R-value before choosing the product.\"\n    },\n    {\n      \"@type\": \"HowToStep\",\n      \"position\": 3,\n      \"name\": \"Check the depth before you quote\",\n      \"text\": \"Compare the settled thickness the chart requires for your target R-value against the cavity depth you actually have. Where the cavity is shallower, either the assembly changes or the R-value does.\"\n    },\n    {\n      \"@type\": \"HowToStep\",\n      \"position\": 4,\n      \"name\": \"Divide the area by the coverage and round up\",\n      \"text\": \"Divide net area by the maximum net coverage per bag or per bundle at your target R-value, then round up to a whole unit and add for cut waste.\"\n    }\n  ]\n}\n<\/script><br \/>\n<script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"FAQPage\",\n  \"mainEntity\": [\n    {\n      \"@type\": \"Question\",\n      \"name\": \"How many bags of blown insulation do I need for R-30?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Divide area by the coverage on the bag. 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Bag counts, bundle counts, and the climate zone check update as you type. Pricing the whole job? Estimate it from a photo in about six seconds. &#9733;&#9733;&#9733;&#9733;&#9733; 4.8 [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_focuskw":"insulation calculator","_yoast_wpseo_title":"Insulation Calculator: Bags, Batts, and R-Value by Zone","_yoast_wpseo_metadesc":"An insulation calculator for bag counts, batt bundles, cavity depth, and the climate zone R-value, the quantities behind insulation cost per square foot.","_yoast_wpseo_linkdex":"71","_yoast_wpseo_content_score":"90","_yoast_wpseo_meta-robots-noindex":"","_yoast_wpseo_canonical":"","inline_featured_image":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-9453","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v21.2 - 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