Concrete Wall Calculator
Find how many cubic yards or bags of concrete a poured wall needs.
Measure your project
Your answer
That is 117.3 cubic feet. We added 10% extra.
If you buy bags
One 80 lb bag makes 0.6 cubic feet of concrete.
If you order a truck (ready-mix)
Ask for 4.50 cubic yards. We round up to the next quarter yard.
This answer is a guide. Basement and retaining walls hold back soil. Check your local building rules or ask a builder or engineer.
Which costs less?
You also skip mixing 196 bags by hand. Have the wooden edges (forms) ready before the truck comes.
Prices are US middle prices from October 2026. Ask your store for their price.
Quick answers
- A 20 × 8 ft wall, 8 in thick
- 4.35 cubic yards with 10% extra. We round that up to 4.50 for a truck order.
- Thinnest basement wall
- 6 in with no vertical bars, for an 8 ft wall holding back 4 ft of soil (IRC).
- How high above the ground?
- At least 6 in. Or 4 in where brick or stone covers the wall.
- What strength?
- 2,500 psi if the wall is out of the weather. Up to 3,000 psi if it is not.
- Building with blocks?
- This page is for poured walls. Counting blocks? Try the concrete block calculator.
How to work it out
- Measure how long and how high the wall is, in feet.
- Measure how thick it is in inches, then divide by 12 to get feet.
- Multiply length × height × thickness to get cubic feet.
- Add 10% extra. Then turn cubic feet into cubic yards: ÷ 27.
- We round up to the next quarter yard. Ask your plant how it sells.
8 in ÷ 12 = 0.667 ft
20 × 8 × 0.667 = 106.7 cubic feet
Add 10%: 117.3 cubic feet
117.3 ÷ 27 = 4.35 cubic yards. Round up: 4.50.
Cubic yards for common wall sizes
Find your wall's length and height on the left. Then read across to its thickness. The height is the full height of the concrete.
| Wall | 6 in thick | 8 in thick | 10 in thick | 12 in thick |
|---|---|---|---|---|
| 10 × 4 ft | 0.81 | 1.09 | 1.36 | 1.63 |
| 20 × 4 ft | 1.63 | 2.17 | 2.72 | 3.26 |
| 20 × 8 ft | 3.26 | 4.35 | 5.43 | 6.52 |
| 40 × 8 ft | 6.52 | 8.69 | 10.86 | 13.04 |
| 100 × 8 ft | 16.30 | 21.73 | 27.16 | 32.59 |
Pour the footing under the wall too? Add it in step 1 of the calculator.
At 8 in thick, one cubic yard makes about 40.5 sq ft of wall face.
How thick should the wall be?
The IRC (the US home building code) sets basement wall thickness by the soil and the backfill. Backfill is how much higher the ground is outside than the floor inside.
| Backfill | Gravel or clean sand | Silty sand or silty gravel | Clayey sand or lean clay |
|---|---|---|---|
| 4 ft | 6 in | 6 in | 6 in |
| 5 ft | 6 in | 8 in | 8 in |
| 6 ft | 8 in | 8 in | 10 in |
| 7 ft | 8 in | 10 in | 10 in |
| 8 ft | 10 in | 10 in | 12 in |
Thinner walls are allowed with vertical bars. Thicknesses are nominal. The code bars this table for soils not shown.
Say you have 6 ft of backfill in clayey sand or lean clay. With 2,500 psi concrete, the wall needs to be 10 in thick to skip vertical bars.
Our calculator's first wall is 8 in thick. In this table, that skips vertical bars for up to 5 ft of backfill in any of the three soils.
The IRC's wall tables call for horizontal #4 bars. One goes within 12 in of the top, and one near mid-height (8 ft walls).
A basement wall must also be at least as thick as the wall it holds up.
Before the soil goes back
- The top of the wall must stand at least 6 in above the ground. Where brick or stone covers it, 4 in is enough.
- A wall that will hold 4 ft of soil or more needs support at the top and bottom first. Below that, no bracing is needed.
- A wall needs an engineer if groundwater pushes on it. Another case: it holds back over 48 in of soil, with no lasting support at the top or bottom.
These walls hold back soil and carry the house. Check your local building rules or ask a builder or engineer.
What strength of concrete?
Concrete strength is given in psi. The IRC sets it by how much weather the wall faces.
- Out of the weather: 2,500 psi.
- Open to the weather: 2,500 psi with very little (negligible) weathering. 3,000 psi with moderate weathering. 3,000 psi with severe weathering.
- Earthquake areas rated D0, D1 or D2: 3,000 psi.
In moderate and severe areas, walls open to the weather also need air-entrained concrete. That mix has tiny air bubbles in it.
Ready-mix plants price concrete by its psi, so say the number when you order. Our truck price is $179 a cubic yard for 3,000 psi. We took the middle price from 5 US sellers in Oct 2026.
The 20 × 8 ft example wall is 5.50 cubic yards short of a full truck (about 10). For that gap, plants may charge a fee. The 4 cost guides we found range from $30 to $80 per cubic yard.
Building a block wall instead?
A block wall needs blocks and mortar, and may need grout in some cores. This page doesn't count those.
The block makers' group (CMHA) counts 1.125 blocks for each square foot of wall face. So a 20 × 8 ft block wall takes 180 blocks, before extra.
Count them with the concrete block calculator. To fill the cores, use the block fill calculator.
Questions people ask
How do I work out concrete for a wall?
Multiply length × height × thickness, with all three in feet. Turn that into cubic yards by dividing by 27. Sakrete suggests ordering about 10% more.
How much concrete for a 20 × 8 ft wall?
At 8 in thick, 3.95 cubic yards. With 10% extra, 4.35 cubic yards.
How thick should a concrete wall be?
For an 8 ft basement wall, it depends on the soil and how high it is piled outside. The IRC table on this page shows 6 to 12 in with no vertical bars. It must also be at least as thick as the wall above it.
Does a concrete basement wall need rebar?
Yes. The IRC's wall tables call for horizontal #4 bars. Vertical bars depend on the wall thickness, the soil and the backfill.
How much does it cost to build a concrete wall?
We can only price the concrete. For a 20 × 8 ft wall, 8 in thick, a truck costs about $1,067. That uses the middle truck price of 5 sellers ($179 a cubic yard). It adds a rough small-order fee from 4 cost guides. Forms, bars and labor cost more.
How many bags of concrete for a wall?
A 10 × 4 ft wall, 8 in thick, takes 49 bags of 80 lb with 10% extra. For bigger walls, step 3 shows when a truck costs less.
What psi concrete for a foundation wall?
The IRC asks for at least 2,500 psi. In earthquake areas rated D0, D1 or D2, it is 3,000 psi.
When does a wall need an engineer?
The IRC asks for one when groundwater pushes on the wall. It also does for a wall holding back over 48 in of soil. That is when the wall has no lasting support at the top or bottom.
Where our numbers come from
- Bag sizes and weight: Quikrete Concrete Mix data sheet
- Extra for spills: Sakrete slab calculator (10%)
- Poured concrete walls: US home building code (IRC R404)
- Concrete strength by use: US home building code (IRC Table R402.2)
- Blocks, mortar, sand and core fill: Concrete Masonry & Hardscapes Association (TEK 04-02A)
- Bag price: the middle price of 9 US stores (Oct 2026)
- Truck price: the middle price of 5 US concrete sellers (Oct 2026)
- Small-order fee: the middle of 4 US cost guides (2026)
Made by BuildersCount. Last checked 3 Oct 2026.
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