Concrete Calculator
Calculate how much concrete you need for a slab, footing, or pour.
Try an example
1.235 cubic yards
About this calculator
How This Concrete Calculator Works
Enter the length, width, and depth of a slab or pour, and the calculator returns the volume of concrete needed, plus how many standard bags that translates to.
Worked Example
A 10 ft × 10 ft slab poured 4 inches deep needs about 1.23 cubic yards of concrete — roughly 56 standard 80 lb bags.
The Formula
Volume = Length × Width × Depth, with depth converted from inches to feet first. Ready-mix concrete is typically ordered by the cubic yard, while bagged concrete coverage is usually given in cubic feet per bag — this calculator converts between both so you can order either way.
Ordering Extra
Most contractors add 5-10% beyond the calculated volume to account for spillage, an uneven or slightly low sub-base, and general measurement imprecision — running short mid-pour is a bigger problem than having a small amount left over, since concrete needs to be poured continuously to avoid weak seams.
Ready-Mix vs. Bagged Concrete
For anything beyond roughly 1 cubic yard, ready-mix delivery is usually more practical, consistent, and cost-effective than hand-mixing dozens of bags. Bagged concrete is best suited to small jobs — post footings, small patches, or a single stepping stone — where a delivery truck wouldn't make sense.
Worked example
A 10 ft × 10 ft slab poured 4 inches deep needs about 1.23 cubic yards of concrete — roughly 56 standard 80 lb bags.
Frequently asked questions
Should I order extra concrete beyond the calculated amount?
Yes — most contractors add 5-10% to account for spillage, an uneven sub-base, and small measurement inaccuracies, especially for irregularly shaped pours.
When should I use ready-mix instead of bagged concrete?
For anything beyond roughly 1 cubic yard, ready-mix delivery is usually more practical and cost-effective than mixing dozens of bags by hand — bagged concrete is best suited to small jobs like post footings or patch repairs.