Concrete Calculator

Length, width and depth — cubic yards and bag count for your pour.

ft
ft
in
Concrete needed
1.235 yd³
Cubic feet
33.33
80 lb bags needed
56

Always buy a little extra — a 5-10% margin covers spillage and uneven subgrade. Bag yields shown are standard for premixed concrete; check your specific bag's label.

A worked example

A 10×10 ft slab at 4 inches thick needs about 1.23 cubic yards of concrete — exactly 56 bags of 80 lb premix.

Frequently asked questions

Why does bag count change so much with bag size?

An 80 lb bag yields about 0.6 cubic feet, a 60 lb bag about 0.45, and a 40 lb bag about 0.3 — roughly proportional to weight. Smaller bags mean more bags needed for the same total volume, plus more individual mixing.

Should I order exactly the calculated amount?

No — always add a margin. Uneven subgrade, form leaks, and minor spillage are normal, and running short mid-pour is a bigger problem than having a little extra. Many contractors add 5-10% on top of the calculated volume.

Bag yields shown are standard estimates — always verify against the yield printed on your specific bag, since fast-setting or fiber-reinforced mixes can vary.