Concrete Calculator
Calculate cubic yards of concrete for slabs, footings, columns, and steps — including waste allowance and bag counts.
Your details
Ordering
This calculator runs entirely on your device. Nothing you enter is uploaded, stored, or sold. How this works
Concrete needed
3.26 yd³
2.96 yd³ net plus 10% waste — order 3.50 yd³
Includes your inputs, the full breakdown, and every row of the table.
Cubic feet
88.0 ft³
Bags needed
147
80 lb bags
Estimated ready-mix cost
$538
At $165/yd³
Surface area
240.0 ft²
- Net volume
- 2.963 yd³
- Waste allowance (10%)
- 0.296 yd³
- Total to order
- 3.50 yd³
- Ready-mix cost
- $578
- Or 147 bags
- $955.50
What this means
- Above roughly one cubic yard, ready-mix delivery is cheaper and far easier than mixing bags. Most suppliers have a short-load fee under 3-4 yards.
- A 4-inch slab is standard for patios and walkways; use 5-6 inches with rebar for driveways and anything carrying vehicle loads.
- Order slightly more than you need. Running short mid-pour creates a cold joint you cannot undo.
How the concrete calculation works
Concrete is sold by the cubic yard, which is 27 cubic feet. The calculation is simply length times width times thickness, with thickness converted from inches to feet by dividing by twelve. Round shapes use πr²h instead.
Always add a waste allowance. Sub-grade is never perfectly level, forms bow slightly, and some concrete stays in the chute and the wheelbarrow. Ten percent is standard for a well-prepared slab; fifteen is safer for footings dug into uneven ground.
Frequently asked questions
How many bags of concrete are in a yard?
Forty-five 80 lb bags, sixty 60 lb bags, or seventy-two 50 lb bags. That is a lot of mixing — which is why ready-mix is standard above one cubic yard.
How thick should a concrete slab be?
Four inches for patios, sidewalks, and sheds. Five to six inches with reinforcement for driveways, garages, and anything supporting vehicles.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.