Skip to content
Calculators & guides

Concrete Footing Calculator

Estimate concrete for strip footings under walls or a set of identical pad footings for a deck or addition. For round piers, use the round footing calculator.

Units

Geometry dimensions — schematic, not to scaleL (length)HW
Schematic · not to scale · quantity repeats the entire solid

Concrete & bag assumptions

Density is the placed concrete density, not dry bag weight. Defaults are examples for normal-weight concrete. Bag weight does not determine yield; use the mixed yield printed on your product.

Estimate cost (optional · USD)

All cost fields are optional and user-entered. Ready-mix and bags are alternatives, never added together. No average or local prices are assumed — use a real quote. Labor per area is available only for shapes with a defined footprint.

Formula & solid model

Volume = length × width × depth × quantity

All lengths convert to metres before calculation. Blank waste = 0%. Zero dimensions or quantity produce zero volume. Display values are rounded; costs and bags use unrounded volumes.

Footing · incl. 10% waste

You need approximately 0.724 cubic yards

19.556 ft³ · 0.554 m³ · 553.75 litres

Volume

UnitExact+10% waste
Cubic yards0.6580.724
Cubic feet17.77819.556
Cubic metres0.5030.554
Litres503.411553.752

Placed weight · incl. waste

2,933.33 lb / 1,330.54 kg

Density: 150 lb/ft³ · weight = volume × density

Selected premix bags · incl. waste

33 × 80 lb bags

Yield: 0.6 ft³ / bag · total volume ÷ yield, rounded up.

Estimate inputs & formula

Length: 20 ft · Width: 16 in · Depth: 8 in · Number of footings: 1

Volume = length × width × depth × quantity

Estimate only, not engineering advice. Actual needs vary with subgrade, forms and spillage. Confirm final quantities and product yields with your supplier or contractor before ordering.

What this calculates

Footings are rectangular prisms, often with a long length and narrow width. Enter the total run for a continuous footing, or the size of one pad and the number of pads.

Formula

Volume = length × width × depth × number of footings

Worked example

40 ft strip footing, 16 in wide × 8 in deep

  1. 1.40 × 1.333 × 0.667 = 35.6 cu ft
  2. 2.35.6 ÷ 27 = 1.32 cu yd
  3. 3.Add 10%: about 1.45 cu yd

Common mistakes

  • Measuring the wall length instead of the footing centerline around corners, which double-counts corners.
  • Ignoring over-dig — trenches are rarely perfectly square, so extra waste is sensible.
  • Guessing footing size. Footing dimensions depend on loads and soil; follow your plans or local code.

Frequently asked questions

How deep should footings be?

Depth depends on frost line, soil and load and is set by local building code or an engineer. This calculator only estimates volume for the size you enter.

Should I use more waste for trench footings?

Many builders use 10–15% for footings poured against earth because trench walls are irregular.