Construction
Concrete Calculator
Enter your dimensions to calculate the volume of concrete needed in cubic yards and cubic feet, plus an estimate of 40, 60, or 80 lb bags — with a waste allowance so you don't come up short on pour day.
Quick answer: Concrete is sold by the cubic yard (27 cubic feet). A 10×10 slab at 4 inches thick needs about 1.23 cubic yards, or roughly 56 80-lb bags.
- Volume (no waste)33.3 cu ft
- With 10% waste36.7 cu ft
- Cubic yards1.36
- 80 lb bags to buy62
One cubic yard = 27 cubic feet. For more than about a cubic yard, ready-mix delivery is usually cheaper and faster than mixing bags. Order a little extra — you can’t add to a short pour.
How it works
1. Pick a shape
Slabs and footings are length × width × thickness; columns are π × radius² × height. Enter thickness in inches — the calculator converts to feet.
2. Convert to yards
Concrete is sold by the cubic yard (27 cubic feet). Ready-mix trucks and pricing are quoted per yard.
3. Add waste
A 5–10% overage covers uneven subgrade and spillage. For bagged mixes, an 80 lb bag yields about 0.6 cubic feet.
Frequently asked questions
How many cubic yards of concrete do I need?
Multiply length × width × thickness (all in feet) to get cubic feet, then divide by 27 for cubic yards. The calculator does this and adds a waste margin.
How many bags of concrete in a yard?
About 45 bags of 80 lb mix, 60 bags of 60 lb, or 90 bags of 40 lb make one cubic yard. For anything more than a few yards, ready-mix is usually cheaper than bags.
How thick should a concrete slab be?
Four inches is standard for patios and walkways; driveways and areas bearing vehicles typically need 5–6 inches over a compacted base.