Contractor Calculator · Retaining Walls
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
Belgard Highland Stone and Diamond Pro sizes, read October 13, 2026.
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.
Retaining wall calculator: price it
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.
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
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Measure the run and the drop
Length along the face, exposed height at the tallest point.
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Pick the block before the count
Block height sets the course count and the buried course.
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Dig for the pad and the buried course
The trench runs 12 in wider than the block and 6 in below its bottom.
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Order block, cap and stone together
One delivery keeps the color lot matched.
Try SimplyWise Cost Estimator free and quote the wall from a photo.
Keep reading
Sources
- Belgard Technical Resource Guide, retaining wall installation (burial, pad, drainage, pipe; 2026-10-13).
- Belgard, Highland Stone (size, gravity limit; 2026-10-13).
- Belgard Diamond Pro spec sheet BEL22-412 (sizes, gravity limit; 2026-10-13).
- Oldcastle APG, Belgard 12 x 4 x 18 in wall cap (2026-10-13).
- Washington State DOT Design Manual, Exhibit 620-1 (1.85 tons per yard; 2026-10-13).
- City of Saint Paul, Retaining Walls (2026-10-13).
- City of Inver Grove Heights, Retaining Walls (2026-10-13).
- SimplyWise Cost Estimator, App Store (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.
Turn the wall takeoff into a signed quote.
Snap a photo and get an itemized estimate in about 6 seconds. Free to try.