Concrete Calculator
Free concrete calculator: concrete volume for a slab, footing or round column in cubic yards, cubic feet or cubic meters, and the premixed bags you need.
Premixed bags
Bag yields: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft, 40 lb ≈ 0.30 cu ft, 25 kg ≈ 12 L, 40 kg ≈ 19 L. Check the yield printed on your bag.
What it does
Concrete is ordered and sold by volume: cubic yards in the United States, cubic meters elsewhere. A slab is length × width × thickness and a round column is π × radius² × height. The calculator adds a margin for spills, uneven ground and the formwork, and converts the volume into premixed bags for small jobs. A 10 × 10 ft slab 4 inches thick needs 1.23 cubic yards, or 56 bags of 80 lb.
How to use it
- Choose a slab or a round column, and metric or imperial units.
- Type the measurements, how many pieces and the margin for waste (5 to 10% is common).
- Read the volume to order and the number of premixed bags.
The arithmetic runs in your browser. Nothing you type is sent anywhere and nothing is stored, so you can use these with real numbers.
Frequently asked questions
How much extra concrete should I order?
Usually 5 to 10%. Uneven ground, a thicker slab at the edges and concrete left in the truck or the mixer all use more than the exact volume, and running short in the middle of a pour is worse than a little left over.
Bags or ready-mix truck?
Bags make sense up to about 1 cubic yard (0.75 m³), for posts, small pads and repairs. Above that, a ready-mix truck is usually cheaper and gives a more even pour.
How thick should a slab be?
Patios and walkways are often 4 inches (10 cm); driveways for cars 5 to 6 inches (12 to 15 cm). Structural slabs and footings follow the engineer's design.
How many cubic feet are in a cubic yard?
27, because a yard is 3 feet and 3 × 3 × 3 = 27. One cubic yard is 0.765 cubic meters.