Concrete
Concrete Wall Calculator
Enter the wall dimensions and the total area of any windows or doors to deduct.
Over-excavation, spillage and uneven subgrade. 5-10% for formed work, 10-15% on rough ground.
Yields are the figures printed on the bag. Speciality mixes differ — check yours.
Optional. Leave at zero to skip the cost estimate.
Material quantity estimate for planning and purchasing. Not structural engineering advice, not a bid, and not a code determination.
Wall thickness
Eight inches is the residential default for a poured foundation wall, and it is what most forming systems are built around. Six inches is the practical minimum and is used for short stem walls and frost walls. Ten to twelve inches shows up on tall basement walls, walls retaining significant backfill, and anything carrying unusual load.
| Use | Thickness | Notes |
|---|---|---|
| Stem wall, frost wall | 6-8 in | Vertical #4 bar at 48 in |
| Basement wall to 8 ft | 8 in | Bar per IRC tables by backfill height |
| Basement wall over 9 ft | 10-12 in | Engineered |
| Retaining wall under 4 ft | 8-10 in | Drainage and weeps required |
| Retaining wall over 4 ft | Engineered | Permit and design required |
Retaining walls over four feet
The IRC exempts retaining walls under 4 feet of retained height from engineered design. Above that, a retaining wall is holding back a soil mass that pushes with real force, and it needs a designed section, drainage and usually a permit. This calculator will give you a volume for any wall you describe; it does not tell you the wall will stand.
Drainage is what kills retaining walls that were otherwise built correctly. Free-draining backfill, a perforated drain at the base, and weeps through the face — hydrostatic pressure behind an undrained wall will move concrete.
Ordering
A 30 x 8 ft wall at 8 inches is 160 cubic feet, just under 6 cubic yards — comfortably into ready-mix territory. Forms are the constraint on a wall pour, not concrete: pour in lifts of 3-4 feet, vibrate each lift, and do not let a lift set before the next goes on or you get a cold joint through the wall.
Common questions
How much concrete for a 30 ft wall?
A 30 ft wall 8 ft tall and 8 inches thick is 160 cubic feet, or 5.93 cubic yards. With 10% waste, order 6.5 yards.
How thick should a poured concrete wall be?
Eight inches for a standard residential foundation wall up to 8 ft tall. Six inches for short stem and frost walls. Ten to twelve inches for tall basement walls or significant retained backfill, and those get engineered.
Do I need a permit for a retaining wall?
In most jurisdictions, yes above 4 feet of retained height, and often above 3 feet. Below that it is usually exempt. Check locally before building — retrofitting a failed wall costs many times what the permit did.