# Roof Pitch Calculator Canonical URL: https://www.simplywise.com/blog/roof-pitch-calculator/ Plain text: https://www.simplywise.com/blog/roof-pitch-calculator/llms.txt Publisher: SimplyWise, Inc. (https://www.simplywise.com) Published: September 16, 2026 Updated: October 27, 2026 Summary: A roof pitch calculator that turns rise over a 12 inch run, a measured rise and run, or an angle into pitch, slope angle, and true roof area. --- Log in (https://simplywise.com/login) ## Roof Pitch Calculator: Pitch, Angle, and Roof Area Roof pitch is rise over a 12 in run. Set the rise below, or type a measured angle, and the pitch, multiplier, and true roof area update as you type. Add SimplyWise as a preferred source (https://www.google.com/preferences/source?q=simplywise.com) Set the pitch, get the angle and the real roof area Common pitch Rise (in) Run (in) Leave at 12 for a standard pitch Measured angle (degrees) Overrides rise and run Roof plan area (sq ft) 6 in 12 roof pitch Slope angle26.6 degrees Pitch multiplier1.118 Roof surface area1,789 sq ft Standard slope for asphalt shingles, single underlayment, per IRC R905.2.2. Code limits read September 11, 2026. At a glance 1. Roof pitch is rise in 12. A roof climbing 6 in over 12 in of run is a 6:12. 2. Slope angle is the arctangent of rise over run. A 6:12 is 26.6 degrees. 3. The pitch multiplier is the square root of 1 plus the ratio squared. A 6:12 is 1.118. 4. Plan area times the multiplier is the real surface you cover. 5. IRC R905.2.2 sets 2:12 as the shingle floor, with double underlayment below 4:12. 6. TAMKO, IKO, and CertainTeed publish the same 2:12 floor. ## How the roof pitch calculator works Pitch is a ratio. Roofers write it as rise in 12, inches of climb for every 12 in of run. Level a square against a rafter, mark 12 in out, and measure straight up. Two numbers fall out of that ratio. Slope angle is the arctangent of rise over run in degrees. The pitch multiplier is the square root of 1 plus the ratio squared, the hypotenuse of the same triangle. The multiplier is the one that touches money. A plan draws the roof flat, so plan area is always smaller than the surface you cover. ## Worked example: a 6:12 roof over a 1,600 sq ft footprint A 6:12 climbs 6 in over 12 in of run, a ratio of 0.5. The arctangent of 0.5 is 26.6 degrees. The multiplier is the square root of 1.25, or 1.118. Multiply the 1,600 sq ft footprint by it and the roof surface is 1,789 sq ft, about 189 sq ft more than the plan shows. Bid the plan area instead and you are short almost two squares of shingles, underlayment, and labor. On a 12:12 that footprint covers 2,263 sq ft. ## Pitch multiplier table Geometry, so these never change. The last column applies the multiplier to a 1,600 sq ft footprint. | Pitch | Angle | Multiplier | Roof area on 1,600 sq ft | | --- | --- | --- | --- | | 2:12 | 9.5 degrees | 1.014 | 1,622 sq ft | | 4:12 | 18.4 degrees | 1.054 | 1,687 sq ft | | 5:12 | 22.6 degrees | 1.083 | 1,733 sq ft | | 6:12 | 26.6 degrees | 1.118 | 1,789 sq ft | | 8:12 | 33.7 degrees | 1.202 | 1,923 sq ft | | 9:12 | 36.9 degrees | 1.250 | 2,000 sq ft | | 10:12 | 39.8 degrees | 1.302 | 2,083 sq ft | | 12:12 | 45.0 degrees | 1.414 | 2,263 sq ft | ## Where low slope starts, and what the code makes you do IRC R905.2.2 is short and blunt. Asphalt shingles are allowed only on roof slopes of two units vertical in 12 units horizontal or greater. From 2:12 up to 4:12, double underlayment is required. The makers publish the same floor. TAMKO lists Elite Glass-Seal for decks with inclines of 2 in per foot or greater, and sends 2 in to under 4 in per foot to its low slope section. IKO prints it on the Cambridge sheet: never apply asphalt shingles to slopes less than 2:12. CertainTeed limits Landmark to slopes greater than 2 in per foot, with additional underlayment below 4:12. So 4:12 is where a shingle roof stops needing special treatment, and 2:12 is where shingles stop being legal. Below that you change coverings: a membrane, standing seam metal down to 1/4:12, or lapped seam panels with sealant down to 1/2:12. ## Turn the pitch into a priced roof The calculator gives you the real surface area. 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. ## Minimum pitch by roof covering Chapter 9 sets a floor for every covering, not just shingles. | Covering | Minimum slope | Section | | --- | --- | --- | | Asphalt shingles | 2:12, double underlayment below 4:12 | R905.2.2 | | Clay and concrete tile | 2.5:12, double underlayment below 4:12 | R905.3.2 | | Metal roof shingles | 3:12 | R905.4.2 | | Wood shingles and shakes | 3:12 | R905.7.2, R905.8.2 | | Lapped seam metal panels | 3:12, or 1/2:12 with lap sealant | R905.10.2 | | Standing seam metal | 1/4:12 | R905.10.2 | ## Measure the pitch without guessing 1. Work off a level, not your eye Hold a 24 in level on the shingles, center the bubble, mark 12 in from the roof end, and measure straight down. That drop is the rise. 2. Measure a rafter instead if the roof is steep From the attic, measure rafter rise and horizontal run to the ridge. Any pair works, and the calculator scales it back to a 12 in run. 3. Check every plane separately Additions, dormers, and porches rarely share the main pitch. Run the calculator per plane and add the areas, because one multiplier across a mixed roof understates the steep half. 4. Convert to squares before you price Roofers buy in squares of 100 sq ft. Divide surface area by 100, then add waste. The 1,789 sq ft example is 17.89 squares before cuts. ## Keep reading - Construction Calculators Hub (https://www.simplywise.com/blog/construction-calculators/) - Roof Replacement Cost (https://www.simplywise.com/blog/roof-replacement-cost/) - Gutter Replacement Cost (https://www.simplywise.com/blog/gutter-replacement-cost/) - Drywall Sheet and Mud Calculator (https://www.simplywise.com/blog/drywall-sheet-and-mud-calculator/) ## Sources ### Code limits - City of Seattle, Residential Code Chapter 9, Roof Assemblies (https://www.seattle.gov/documents/Departments/SDCI/Codes/SeattleResidentialCode/2012SRCChapter9.pdf) (R905.2.2 plus the R905.3.2 through R905.10.2 minimums; verified 2026-09-11). - Town of Windsor Locks CT, Asphalt Shingle Installation handout (https://cdn.townweb.com/windsorlocksct.org/wp-content/uploads/2024/01/Ashpalt_Shingle_Installation.pdf) (R905.2.2, 2:12 floor, double underlayment to 4:12; verified 2026-09-11). ### Shingle maker data sheets - TAMKO, Elite Glass-Seal data sheet (https://www.tamko.com/docs/default-source/data-sheets/TAMKO-3-tab-elite-glass-seal-data-sheet-(joplin).pdf?sfvrsn=a30256a0_29) (inclines of 2 in per foot or greater; low slope from 2 in to under 4 in; verified 2026-09-11). - IKO, Cambridge technical data sheet (https://www.iko.com/na/wp-content/uploads/2024/12/4220XXX_IKO_TDS_Cambridge_EN.pdf) (never apply asphalt shingles to slopes less than 2:12; verified 2026-09-11). - CertainTeed, Landmark product data (https://www.buildsite.com/pdf/certainteed/Landmark-Shingles-Product-Data-2899919.pdf) (slopes greater than 2 in per foot; additional underlayment below 4:12; verified 2026-09-11). ### Product - SimplyWise Cost Estimator, App Store (https://apps.apple.com/us/app/simplywise-cost-estimator/id6670619664) (4.8 rating; verified 2026-09-09). ## Common questions about roof pitch ### Pitch, angle, and area **What is a 6:12 roof pitch in degrees?** 26.6 degrees. Divide the 6 in rise by the 12 in run for 0.5, then take the arctangent in degrees. **How do I find the pitch multiplier?** Take the square root of 1 plus the rise divided by run, squared. A 4:12 is 1.054, a 6:12 is 1.118, and a 12:12 is 1.414. **How do I get roof area from the footprint?** Multiply plan area by the pitch multiplier. A 1,600 sq ft footprint under a 6:12 covers 1,789 sq ft of roof. ### Pitch limits and roofing over them **What is the minimum pitch for asphalt shingles?** 2:12. IRC R905.2.2 allows asphalt shingles only on slopes of 2:12 or greater, and TAMKO, IKO, and CertainTeed publish the same floor. **When does a roof need double underlayment?** From 2:12 up to 4:12. R905.2.2 calls that range low slope and requires two layers of underlayment under the shingles. **Can SimplyWise price a roof from a photo?** 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 or $239.99/yr. 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It is free to try with a 7-day free trial, then $29.99 per month or $239.99 per year (about $20 per month on the annual plan), and one subscription includes every app in the SimplyWise suite. - Download: https://www.simplywise.com/download - App Store: https://apps.apple.com/us/app/simplywise-cost-estimator/id6670619664 - Google Play: https://play.google.com/store/apps/details?id=com.simplywise.costestimator - Every SimplyWise page as plain text: https://www.simplywise.com/blog/llms.txt