Concrete Volume Calculator
Estimate concrete volume and bags needed for slabs and columns.
Working out how much concrete to order
Volume is simply the area of the pour multiplied by its depth. For a rectangular slab that is length × width × thickness; for a round column it is π × radius² × height. Keep every measurement in the same unit before multiplying.
Ready-mix concrete is usually ordered in cubic yards (US) or cubic metres (most other countries). Bagged mix is sold by weight, and yields vary by product, so bag counts here are estimates — always round up and add a waste allowance for spillage and uneven ground.
| 1 cubic yard | 27 cubic feet |
|---|---|
| 80 lb bag | ≈ 0.60 cubic feet |
| 60 lb bag | ≈ 0.45 cubic feet |
A slab 10 ft by 10 ft and 4 inches thick is 100 square feet times 0.33 feet, or about 33.3 cubic feet — roughly 1.23 cubic yards. With a 10% waste allowance that is about 1.36 cubic yards to order.
Ordering concrete with confidence
Concrete is unforgiving once it starts to set, so it is better to have a little too much than to run short mid-pour. A small waste allowance covers spillage, uneven ground and slight over-digging, and means you are not scrambling for an extra bag at the worst possible moment.
Bags or ready-mix?
- Bagged mix suits small jobs of a few cubic feet — posts, small pads and repairs.
- Ready-mix delivery is usually cheaper and far less work once you pass roughly half a cubic yard.
- Mind the working time. Concrete begins to set within a couple of hours, so plan to place and finish it without long gaps.