Concrete Foundation Calculator

Foundation volume formula

For rectangular footings and stem walls, multiply length by width by depth in feet, then divide by 27 to get cubic yards. For round piers, use the cylinder in the calculator (outer diameter and height; inner diameter 0 if the pier is solid).

Cubic feet = Length (ft) × Width (ft) × Depth (ft)
Cubic yards = Cubic feet / 27

When this helps

• Continuous or strip footings: calculate each run from length, width, and depth, then add the sections before applying waste.
• Pier pads and post bases: use round or rectangular inputs for isolated pads, deck piers, and porch supports.
• Stem walls and slab edges: treat each wall or thickened edge as its own rectangle so different heights are not averaged.

How to use it

1. Separate the foundation into sections. List each footing, wall, pier, or thickened slab edge before calculating volume.
2. Enter length and width in feet, thickness in inches. The Rectangular Slab thickness field is inches; the calculator divides by 12. Do not type a feet value such as 0.667 into Thickness.
3. Calculate and add the sections. Do not mix a 16-inch footing and an 8-inch wall in one input.
4. Add waste and verify the design. Add 5–10% for uneven excavation and spillage, then confirm footing size, reinforcement, and code on the drawings.

What the calculator does not decide

It estimates concrete quantity. It does not replace structural design, soil evaluation, rebar layout, inspection, or a permit decision.

Ordering checks

Round ready-mix orders to the supplier’s increment, ask about short-load fees, and confirm truck access before a foundation pour. Bags are realistic only for a handful of piers; a house footing is a truck order.

Many residential foundations use 3000–4000 PSI concrete, but the required mix depends on plans, exposure, code, and engineering — not on this page.