Concrete Calculator
Work out how much concrete you need for a slab, patio, driveway, footing or post holes — in cubic yards, cubic metres and pre-mixed bags, with an allowance for waste.
5–10% is typical for spillage and uneven ground.
Volume = length × width × thickness (slabs) or π × radius² × depth (columns), plus your waste allowance. Bag counts use typical yields printed on US pre-mixed concrete bags (80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³) — check your product, as yields vary. For anything larger than a cubic yard or two, ready-mix delivery is usually cheaper than bags. This is a planning estimate, not a contractor quote.
1.36
Cubic yards
1.038
Cubic metres
36.67
Cubic feet
123
40 lb bags (typical yield)
82
60 lb bags (typical yield)
62
80 lb bags (typical yield)
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How to use concrete calculator
- 1Choose US units (feet and inches) or metric.
- 2Pick a slab or round column, and enter the dimensions and thickness or depth.
- 3Set the waste allowance — 5–10% is typical.
- 4Read the volume and the number of bags, or use the volume to order ready-mix.
About this tool
Concrete volume is length × width × thickness for slabs and footings, or π × radius² × depth for round columns and post holes. A 10 × 10 ft patio, 4 inches thick, needs 33.3 cubic feet — 1.23 cubic yards — before waste. Thickness is usually given in inches in the US, so it's converted for you.
Add 5–10% for spillage, uneven sub-base and over-excavation; you don't want to run short halfway through a pour. Bag counts use typical yields printed on US pre-mixed concrete (an 80 lb bag makes about 0.60 ft³, 60 lb about 0.45 ft³, 40 lb about 0.30 ft³), but check your product, since yields vary.
For more than a cubic yard or two, ordering ready-mixed concrete by the truck is usually cheaper and gives a more consistent pour than mixing dozens of bags. This is a planning estimate for materials only, not a structural specification or contractor quote — reinforcement, sub-base and thickness requirements depend on the job and local codes.
Frequently asked questions
At 4 inches thick, a 10 × 10 ft slab is about 33.3 ft³. With 10% extra that's 36.7 ft³ — roughly 62 bags of 80 lb concrete or 82 bags of 60 lb.
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