Retaining Wall Concrete Calculator
The retaining wall concrete calculator works out how much concrete a wall stem needs from its length, height and thickness. The method is the plain rectangular volume relationship: multiply length by height by thickness, all in feet, to get cubic feet, then divide by 27 to convert to cubic yards, the unit ready-mix is ordered and priced in. A wall 20 feet long, 4 feet high and 1 foot thick contains 80 cubic feet, or about 2.96 cubic yards. The calculation covers the wall stem as a simple box; a footing is a separate rectangular volume you add on, and a wall that steps, tapers or batters can be split into rectangular pieces and summed. Because spillage, over-excavation and the last partial load always eat into the order, most builders add a 5 to 10 percent waste allowance and round up to the next increment the supplier offers. Enter your own length, height and thickness to size a pour, price a supply, or check a contractor's quantity. Every figure here is computed deterministically from the formula shown in full below, with a worked example that reconciles exactly to the calculator so you can follow each step and trust the result.
Concrete volume is length times height times thickness, divided by 27 for cubic yards: V = (L x H x T) / 27. A wall 20 ft long, 4 ft high and 1 ft thick needs 2.96 cubic yards of concrete.
Retaining wall volume formula
V (cubic yards) = (L x H x T) / 27
L = wall length in feet
H = wall height in feet
T = wall thickness in feet
27 = cubic feet in one cubic yard
Length times height times thickness gives the stem volume in cubic feet. Dividing by 27 converts it to cubic yards, the unit concrete is supplied in.
Worked example
A retaining wall stem is 20 feet long, 4 feet high and 1 foot thick.
- Volume in cubic feet = 20 x 4 x 1 = 80
- Volume in cubic yards = 80 / 27
- Volume in cubic yards = 2.96
The wall needs 2.96 cubic yards of concrete before any waste allowance. These are the calculator's default inputs, so the result above matches the widget exactly.
Volume at different heights
Cubic yards for a 20 foot long, 1 foot thick stem at a range of heights.
| Length (ft) | Height (ft) | Thickness (ft) | Cubic yards |
|---|---|---|---|
| 20 | 3 | 1 | 2.22 |
| 20 | 4 | 1 | 2.96 |
| 20 | 6 | 1 | 4.44 |
Measurement and survey standards: US National Geodetic Survey (NOAA).
Retaining wall concrete calculator: frequently asked questions
How do I calculate concrete for a retaining wall?
Multiply the wall length by its height and by its thickness, all in feet, to get the volume in cubic feet, then divide by 27 to convert to cubic yards. A wall 20 feet long, 4 feet high and 1 foot thick holds 80 cubic feet, which is about 2.96 cubic yards of concrete.
Why divide by 27?
Concrete is ordered and priced in cubic yards, but length, height and thickness in feet give a volume in cubic feet. One cubic yard is 3 feet by 3 feet by 3 feet, which equals 27 cubic feet. Dividing the cubic-foot volume by 27 converts it to the cubic yards a supplier quotes.
Should I add a waste allowance?
Yes. Spillage, over-excavation, uneven subgrade and the last partial load mean you almost always use a little more than the theoretical volume. A common allowance is 5 to 10 percent on top of the calculated quantity. Order to the next practical increment your supplier offers so you do not run short mid-pour.
Does this include the footing?
No. This calculation covers the wall stem only, as a simple rectangular volume. A footing is a separate rectangular volume below the stem, usually wider and shallower. Calculate the footing as its own length by width by depth, convert to cubic yards, and add it to the stem volume for the total pour.
What if the wall is not a simple rectangle?
Break it into rectangular sections, find each volume separately, and add them. A wall that steps down a slope, tapers in thickness, or has a battered face can be approximated by several rectangular pieces. For a tapered section, use the average thickness. Sum the pieces to get the total concrete volume.
Official sources
- Measurement, survey and geodetic standards: US National Geodetic Survey (NOAA). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.