# Retaining Wall Calculator: Blocks, Caps, Base, and Drainage Canonical URL: https://www.simplywise.com/blog/retaining-wall-calculator/ Plain text: https://www.simplywise.com/blog/retaining-wall-calculator/llms.txt Publisher: SimplyWise, Inc. (https://www.simplywise.com) Published: October 19, 2026 Updated: October 19, 2026 Category: Project Cost Guides Summary: Free retaining wall calculator: enter length and height for blocks, caps, base gravel, drainage stone and drain pipe, plus a 4 ft permit check. --- ## Retaining Wall Calculator: Blocks, Caps, Base, and Drainage Set the length, the height and the block. The full material list updates as you type. ### Blocks, caps, base gravel, and drainage Wall length (ft) Exposed height (ft) Block (height x face length x depth, inches) Belgard Highland Stone and Diamond Pro sizes, read October 13, 2026. Block height (in) Face length (in) Block depth (in) Cap length (in) Waste factor 196 wall blocks to order, waste included Courses7 (6 exposed, 1 buried) Cap blocks28 Base gravel pad1.3 cu yd (2.4 tons) Drainage stone6.48 cu yd Perforated drain pipe40 ft, 1 outlet Height check4.33 ft footing to cap: over 4 ft: permit in Saint Paul and Inver Grove Heights, often an engineer Pad, burial and drainage rules from the Belgard installation guide. Tons use 1.85 per compacted cubic yard, Washington State DOT. A load or slope above the wall changes the permit line. Wall face (sq ft) Labor $ per sq ft of face Materials $ per sq ft of face $0 before markup Labor$0 Materials$0 Defaults: a SimplyWise Cost Estimator run, October 13, 2026, a 40 ft long, 3 ft tall block wall with soil haul-away: $2,600.00 labor, $2,449.16 materials. A retaining wall calculator counts blocks as wall length in inches divided by the block face, times the courses, plus waste. Courses are the exposed height divided by block height, plus the buried course. At a glance 1. Blocks = (length x 12 / face length) x courses x waste, rounded UP. 2. Bury at least 6 in of the base course. A 6 in block buries one course. 3. The gravel pad is 6 in deep and 12 in wider than the block. 4. Drainage stone sits 12 in behind the block or 24 in from the face, whichever is greater. 5. Over 4 ft tall, expect a permit and often an engineer. ## How the retaining wall calculator works Divide the exposed height by the block height and round up. Then add the buried course. Belgard's guide says to bury the base course at least 6 in. A 6 or 8 in block buries one course. A 4 in block buries two. Each course runs the wall length in inches divided by the face length. Multiply by courses, add waste, round UP. Caps are the wall length divided by the cap length, plus waste. ## Worked example: a 40 by 3 ft retaining wall This is the calculator's math on its defaults: a 6 by 18 by 9 in Highland Stone block. Thirty six inches exposed is 6 courses. One buried course makes 7. Each course is 480 in over 18, or 26.67 blocks. Seven courses is 186.67 blocks. Add 5 percent and you order 196. The caps are 26.67, plus 5 percent, so 28. The pad is 40 ft long, 21 in wide and 6 in deep. That is 35 cubic feet, or 1.3 cubic yards. At 1.85 tons a yard, buy 2.4 tons. At 9 in deep, 24 in from the face beats 12 in behind. A stone zone 15 in wide and 3.5 ft tall is 6.48 cubic yards. ## Retaining wall block sizes in the calculator Sizes and gravity limits as Belgard publishes them, read October 13, 2026. | Block | H x L x D (in) | Per 10 ft course | Gravity limit | | --- | --- | --- | --- | | Highland Stone SRW LG | 6 x 18 x 9 | 6.67 blocks | 4.5 ft | | Diamond Pro Straight Face | 8 x 18 x 12 | 6.67 blocks | 4 ft, buried course included | | Diamond Pro cap | 4 x 17/12 x 10 | Tapered, 17 and 12 in faces | Glued on top | ## What the retaining wall calculator assumes for base and drainage The pad is 3/4 in minus base, at least 6 in deep after compaction. It runs 6 in past the block front and back. Drainage stone is 3/4 in free draining aggregate. The pipe is 4 in perforated, with outlets no more than 50 ft apart. We run the stone the full block height. Your plans may stop it lower. ## Turn the takeoff into a signed quote The calculator gives quantities. SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds, with material pricing from the Home Depot closest to your registered zip. The estimate becomes a branded quote the client signs, then an invoice with a deposit field. Pricing is $29.99/mo or $239.99/yr, about $20/mo on annual, with a 7-day free trial. ## When a retaining wall needs an engineer or a permit Saint Paul requires a permit once any point of the wall tops 4 ft. It measures from the base of the footing to the top of the wall. Inver Grove Heights uses the same 4 ft line, plus any wall carrying a surcharge. Its submittal calls for plans by a licensed structural engineer. The block sets its own limit too. Diamond Pro builds gravity walls to 4 ft, buried course included. Past the gravity height, Belgard's guide recommends geogrid and an engineer. The calculator flags both; check your city's handout. ## Lay out the wall in this order 1. Measure the run and the drop Length along the face, exposed height at the tallest point. 2. Pick the block before the count Block height sets the course count and the buried course. 3. Dig for the pad and the buried course The trench runs 12 in wider than the block and 6 in below its bottom. 4. Order block, cap and stone together One delivery keeps the color lot matched. ## Keep reading - retaining wall cost (https://www.simplywise.com/blog/retaining-wall-cost/) - retaining wall repair cost (https://www.simplywise.com/blog/retaining-wall-repair-cost/) - paver calculator (https://www.simplywise.com/blog/paver-calculator/) - SimplyWise Cost Estimator (https://www.simplywise.com/cost-estimator) ## Sources - Belgard Technical Resource Guide, retaining wall installation (https://static.getfastr.com/62ebb7352a22915f359dbbe2/bfceb77e-cdc9-81e1-8008-3b1640917aaf/files/dd67896c-a5bc-81d4-8008-3b49e3a90466/seo/variants/dd67896c-a5bc-81d4-8008-3b4a371a345c/pages/32.html) (burial, pad, drainage, pipe; 2026-10-13). - Belgard, Highland Stone (https://www.belgard.com/product/highland-stone/) (size, gravity limit; 2026-10-13). - Belgard Diamond Pro spec sheet BEL22-412 (https://gis.sanantonio.gov/OHPSystemDocs/api/Attachments/GetRequestAttachment/%7B80331E98-0000-C71A-90BE-DA8E5F00B6A1%7D) (sizes, gravity limit; 2026-10-13). - Oldcastle APG, Belgard 12 x 4 x 18 in wall cap (https://orders.oldcastleapg.com/caps-coping-edgers/caps/belgard-retaining-wall-12-x-4-x-18-cap) (2026-10-13). - Washington State DOT Design Manual, Exhibit 620-1 (https://wsdot.wa.gov/publications/manuals/fulltext/m22-01/620.pdf) (1.85 tons per yard; 2026-10-13). - City of Saint Paul, Retaining Walls (https://www.stpaul.gov/sites/default/files/Media%20Root/Safety%20%26%20Inspections/DSI.Bldg_RetainingWalls.pdf) (2026-10-13). - City of Inver Grove Heights, Retaining Walls (https://www.ighmn.gov/DocumentCenter/View/6230/Retaining-Wall) (2026-10-13). - SimplyWise Cost Estimator, App Store (https://apps.apple.com/us/app/simplywise-cost-estimator/id6670619664) (4.8 rating). ## Common questions on retaining wall blocks **How many blocks do I need for a 40 ft retaining wall?** At 3 ft exposed with a 6 by 18 in block, 196 blocks. That is 7 courses of 26.67 blocks, plus 5 percent waste. **How deep do you bury the first course?** At least 6 in, per the Belgard installation guide. A 6 or 8 in block buries one full course. A 4 in block buries two. **How much gravel goes under a retaining wall?** A pad 6 in deep and 12 in wider than the block. Under a 40 ft wall of 9 in deep block that is 1.3 cubic yards, or 2.4 tons. **How tall can a retaining wall be without a permit?** Saint Paul and Inver Grove Heights draw the line at 4 ft. A surcharge such as a driveway can trigger a permit at any height. **Can SimplyWise price a retaining wall from a photo?** Yes. SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds. Free to try, $29.99/mo or $239.99/yr. --- ## About SimplyWise SimplyWise, Inc. (New York, NY) builds mobile apps for contractors, tradespeople, and small business owners. The SimplyWise Cost Estimator turns a job site photo into an itemized estimate with labor and material costs in about 6 seconds, and the client signs the branded quote to approve it. It is rated 4.8 on the App Store. 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