Concrete Footing Calculator

This is an estimate, not professional advice. Check your inputs and verify the result against your plans and local building code before you build or order. See terms and disclaimer.

How this calculator works

Choose the footing geometry and enter dimensions taken from the project design. The calculator adds the selected waste allowance, converts volume to cubic yards and rounds bag quantities up. Loads, soil bearing capacity, frost depth, settlement and reinforcement are outside this quantity calculation.

Strip footing

Volume (ft³) = Length(ft) × (Width(in) ÷ 12) × (Depth(in) ÷ 12) × FootingsCubic yards = Volume × (1 + Waste%) ÷ 27 Weight = Volume × 140 lb/ft³

Square pad

Volume (ft³) = Side(ft) × Side(ft) × (Depth(in) ÷ 12) × PadsCubic yards = Volume × (1 + Waste%) ÷ 27 Weight = Volume × 140 lb/ft³

Round pier

Radius (ft) = (Diameter(in) ÷ 2) ÷ 12Volume (ft³) = π × Radius² × (Depth(in) ÷ 12) × PiersCubic yards = Volume × (1 + Waste%) ÷ 27 Weight = Volume × 140 lb/ft³

Worked example

A 40 ft strip footing, 16 inches wide and 8 inches deep (Strip footing type), with a 10% waste allowance. Inputs: Footing length 40 ft, Width 16 in, Depth (thickness) 8 in, Number of footings 1, Waste allowance 10 %. Result: 1.45 yd³ (about 66 × 80 lb bags).

Concrete for common strip footings

Strip footing 16 inches wide and 8 inches deep with a 10% waste allowance. Tap a length to load it above.

Footing length	Concrete needed (yd³)	80 lb bags
20 ft footing	0.72	33	Use →
40 ft footing	1.45	66	Use →
60 ft footing	2.17	98	Use →
80 ft footing	2.9	131	Use →
100 ft footing	3.62	163	Use →
120 ft footing	4.35	196	Use →

Method & assumptions

This calculator handles the three footings you actually pour. A continuous strip footing is a long prism, so its volume is length times width times depth. A square pad footing under a post or column is side times side times depth. A round pier footing, the kind formed in a tube, is a cylinder: pi times the radius squared times the depth. Pick the type, and the calculator uses the right geometry, keeping the length or side in feet and the width, depth and diameter in inches.

Whichever footing you choose, the steps after the volume are the same. We apply the allowance entered by the user and divide by 27 for cubic yards. Bags (40, 60 or 80 lb) are rounded up because the selected product is counted in whole packages. Supplier order increments and delivery terms vary, so the calculator reports measured cubic yards without inventing a purchasing rule. The optional comparison uses only the cited QUIKRETE No. 1101 yields and its approximate 140 pounds per cubic foot unit weight.

Footing width, depth and reinforcement are design inputs, not outputs of this calculator. They depend on loads, soil bearing capacity, settlement, frost depth, geometry and the adopted code. Copy the dimensions from approved plans or a qualified design before using this page as a concrete takeoff. The linked ACI 332 document covers design and construction requirements; this calculator implements only the volume geometry.

Pro tips and common mistakes

Use designed dimensions. Copy width, depth, quantity and reinforcement details from the approved project information. This calculator does not size a footing.
Measure the excavation. Compare the designed section with the excavated dimensions before finalising the volume and user-selected allowance.
Match the packaged product. The displayed bag comparison uses QUIKRETE No. 1101. Use the yield on another product when ordering a different mix.

By Calcnaut

Formula and declared-case checks run during the build; sources are listed for readers to review. Read our method and editorial policy.

Frequently asked questions

How much concrete do I need for a footing?

Find the footing volume, add waste, and divide by 27 for cubic yards. A 40 foot strip footing 16 inches wide and 8 inches deep is about 1.45 cubic yards with 10% waste; a 2 foot square pad 12 inches deep is about 0.16 cubic yards.

How wide and deep should a footing be?

This calculator cannot determine that. Width and depth depend on loads, soil bearing capacity, frost depth, settlement and the adopted code. Use dimensions from approved plans or a qualified design.

What is the difference between a strip, pad and pier footing?

A strip footing runs continuously under a wall, a square pad footing sits under a single post or column, and a round pier footing is a cylinder, usually formed in a tube. This calculator does all three.

Do footings need rebar?

This volume calculator cannot decide that. Use the reinforcement shown by the approved design and adopted requirements; if a grid is specified, the rebar calculator can produce a quantity takeoff from those inputs.

Sources and references

These references and structured source records support the method and material data used on this page.

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