Concrete tools

Footing Concrete Calculator — Volume & Bags

Enter the actual formed dimensions for one or more identical rectangular footings to estimate concrete volume and complete bag quantities.

Multiple identical footings
Metric & imperial inputs
Final-project bag rounding

This device

Saved estimates

Save an estimate to keep it here. Data stays in this browser.

Transparent by design

Rectangular footing concrete formula

Each rectangular footing is treated as a rectangular prism. BuildNumbers calculates one footing from the entered dimensions, multiplies by the quantity of identical footings, and applies the extra allowance only after the net total is known.

Per footingV = length × width × depthTotal netV_net = V × quantityOrder volumeV_order = V_net × (1 + allowance ÷ 100)

The result is a material quantity, not a structural design. Use dimensions from the project plans or other qualified design source.

Worked example

Three identical 10 ft × 2 ft × 8 in footings

This controlled quantity example demonstrates why BuildNumbers totals all identical footings before rounding complete bags. It is not a recommended footing size.

01
One footing10 × 2 × (8 ÷ 12) = 13.333 ft³
02
Three footings13.333 × 3 = 40 ft³
03
Convert to yards40 ÷ 27 = 1.481 yd³
04
80 lb bags40 ÷ 0.60 = 66.667; round up once

Verified result1.481 yd³ and 67 × 80 lb bags at 0% allowance

Confirm the actual project dimensions and selected product yield before ordering.

Common questions

Footing concrete calculator FAQ

Quantity guidance without hidden structural assumptions.

How do I calculate concrete for a rectangular footing?

Multiply the entered footing length, width, and concrete depth after converting them to a consistent unit. Multiply that volume by the number of identical footings, then apply your chosen extra allowance.

Does this calculator tell me how wide or deep a footing should be?

No. BuildNumbers only calculates quantity from dimensions you provide. Footing size, reinforcement, bearing requirements, frost depth, concrete strength, and code compliance must come from the project design and applicable requirements.

How are concrete bags rounded?

The calculator totals the concrete for all identical footings first, applies the allowance, then divides by the selected manufacturer-published bag yield and rounds the final purchase quantity up to a whole bag.

Can I calculate more than one footing at once?

Yes. Enter the number of identical rectangular footings. If footings have different dimensions, calculate each size separately rather than averaging them.

Can I use metric dimensions?

Yes. Metric mode uses meters for footing length and width and centimeters for concrete depth. Switching measurement systems converts the values already entered.

Continue planning

Use the right geometry for the next estimate.

GuideHow Much Concrete for Footings?Formula, bags & scope limits LivePost Hole ConcreteRound holes & post displacement