About the Concrete Calculator
Enter the length, width, and thickness of a slab to get the concrete volume in cubic yards and cubic feet, plus how many 60 lb and 80 lb bags it takes. Includes a waste allowance so you don't run short mid-pour.
How it’s calculated
Volume = length × width × (thickness ÷ 12), in cubic feet; ÷ 27 for cubic yards. Bags from the volume each bag yields.
Example calculation
A 10 × 10 ft slab, 4 in thick, needs about 1.36 cubic yards including 10% waste.
Frequently asked questions
Bags or ready-mix?
Bags suit small jobs (a few square feet); for anything larger, ordered ready-mix by the cubic yard is usually cheaper and easier. Suppliers often have a minimum load.
How much extra should I order?
Around 5–10% over the exact figure covers spillage and an uneven subgrade. Running short during a pour means a cold joint, so it's better to have a little extra.
This is a general material estimate for planning only. Actual quantities vary with waste, offcuts, site conditions, product coverage, and technique. Confirm measurements and coverage rates before ordering, follow local building codes, and round up — running short mid-project is costly.