Concrete Calculator

Estimate concrete for slabs, footings, walls, and round columns. Get ready-mix volume plus rounded-up 60 lb and 80 lb bag quantities, with metric and imperial inputs.

Measurement system

Pour shape

Lengthft Enter a length greater than zero

Widthft Enter a width greater than zero

Thickness / depthin Use the actual compacted pour thickness. Enter a depth greater than zero

Number of identical pourscount Enter a whole number from 1 to 10,000

Waste / overage% Accounts for uneven subgrade, spillage, and small measurement errors. Use a percentage from 0 to 50

Calculation Results

Concrete required including overage

—yd³

Ready-mix volume and approximate premix bag quantities.

How to calculate concrete accurately

Choose the pour shape

Use rectangular for slabs, walls, strip footings, and beams. Use round for cylindrical columns, piers, or circular post holes.

Measure finished dimensions

Measure inside the forms. For an irregular slab, divide it into smaller rectangles, calculate each one, and add the volumes.

Enter quantity and overage

Quantity repeats the same shape. The overage percentage is added after all pours are combined; use a value appropriate to subgrade accuracy and job conditions.

Order by volume or whole bags

Ready-mix is shown by volume. Premix bags are always rounded up because a fraction of a sealed bag cannot normally be purchased.

Concrete volume formulas

The calculator first finds the geometric volume, multiplies it by the number of identical pours, and then applies the selected overage. It does not estimate structural strength, reinforcement, delivery fees, or mix design.

Rectangular volume = Length × Width × Depth

Round volume = π × (Diameter ÷ 2)² × Height

Adjusted volume = Geometric volume × (1 + Overage ÷ 100)

Cubic yards = Cubic feet ÷ 27

Bag quantities use approximate yields of 0.60 ft³ for an 80 lb bag and 0.45 ft³ for a 60 lb bag. Product yield can vary, so confirm the yield printed on the concrete mix you will actually buy.

Common concrete volume examples

Geometric volume before adding overage.

Pour	Cubic feet	Cubic yards	80 lb bags
10 × 10 ft slab, 4 in thick	33.33	1.23	56
12 × 12 ft slab, 4 in thick	48.00	1.78	80
20 × 20 ft slab, 4 in thick	133.33	4.94	223
12 in diameter × 3 ft column	2.36	0.09	4

Methodology, assumptions and sources

All dimensions are converted at full precision before volume is calculated; rounding happens only for display. Bag results are planning estimates and are rounded up. ACI defines concrete yield as the volume produced by a batch, while actual yield depends on measured fresh-concrete density.

Sources:

American Concrete Institute — What is yield? — concrete yield definition.
QUIKRETE — Mixing and placing concrete training — approximate 60 lb and 80 lb bag yields.
NIST Handbook 44, Appendix C (2026) — exact customary and metric volume conversions.

Last reviewed: August 2026. These organizations provide reference information and do not endorse Efficienco.

Frequently asked questions

How much extra concrete should I order?

A small overage is commonly added for uneven subgrade, form variation, spillage, and measurement error. The appropriate percentage depends on the job; this calculator leaves it adjustable instead of assuming that one percentage fits every pour.

How many cubic feet are in one cubic yard of concrete?

One cubic yard contains exactly 27 cubic feet. Divide cubic feet by 27 to obtain cubic yards.

How many 80 lb bags make a cubic yard?

Using an approximate yield of 0.60 cubic foot per 80 lb bag, one cubic yard requires 45 bags before any overage because 27 ÷ 0.60 = 45.

Can this calculator design a structural slab or footing?

No. It estimates quantity only. Slab thickness, reinforcement, concrete strength, joints, drainage, frost depth, and footing dimensions should follow the project specification and applicable local requirements.