CONCRETE & MASONRY
Concrete estimating guide
A slab estimate is a volume calculation. Getting the thickness, the units and the allowance right avoids a short or an expensive over-order.
Calculate volume in cubic yards
Multiply length, width and thickness, all in feet, to get cubic feet. Divide by 27 to convert to cubic yards, which is how ready-mix concrete is usually ordered in the United States.
Thickness is usually given in inches. Divide by 12 first. A 10 ft by 10 ft slab that is 4 in thick is about 1.23 cubic yards before any allowance.
Plan for uneven ground and spillage
Subgrades are rarely perfectly level, forms can shift, and some concrete stays in the truck or is lost during placement. A modest allowance helps cover this, and your supplier can advise what is typical for your job.
Thicker edges, footings or reinforcement can change the volume. Add those sections separately.
What this estimate does not cover
This is a volume estimate only. It does not design the slab, choose a mix, or replace local code, reinforcement or engineering requirements.
Confirm the mix, delivery minimums and placement details with a qualified supplier or contractor before ordering.