🧱 Concrete Calculator
Enter the length and width in feet and the thickness in inches. You get the volume and how many premix bags or cubic yards to order.
How the Concrete Calculator works
Volume is length × width × thickness (converted to feet). A cubic yard is 27 cubic feet. Typical bag yields are about 0.30 ft³ (40 lb), 0.45 ft³ (60 lb) and 0.60 ft³ (80 lb). A waste allowance covers spills and uneven ground.
Step-by-step calculation
- 1Measure length and width in feet and thickness in inches.
- 2Multiply for cubic feet.
- 3Divide by 27 for cubic yards.
- 4Add waste and convert to bags.
Worked example
A 10 × 10 ft slab, 4 inches thick: 33.33 ft³ = 1.23 yd³. With 10% extra that is 36.67 ft³ — about 62 bags of 80 lb, or 1.36 cubic yards from a ready-mix truck.
Concrete Calculator examples
| Length (ft) | Concrete needed |
|---|---|
| 5 | 0.68 cubic yards |
| 8 | 1.09 cubic yards |
| 10 | 1.36 cubic yards |
| 13 | 1.77 cubic yards |
| 15 | 2.04 cubic yards |
Other inputs kept at the calculator's default values. Results calculated by this calculator.
Why use a Concrete Calculator?
Order the right amount of concrete — not too little mid-pour.
Important factors that can affect your results
- Uneven ground and form bowing.
- Bag yield varies by brand.
- Rebar and mesh take up little space.
Frequently asked questions
How thick should a patio slab be?
Four inches is common for patios and walkways; driveways are often 4–6 inches. Check local codes.
Bags or ready-mix?
For more than about 1 cubic yard, ready-mix delivery is usually easier and often cheaper.
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Last reviewed November 2026 · How we build and check our tools · Report a problem