Concrete Slab Calculator

Concrete Slab Calculator

Ordering ready-mix concrete requires knowing your exact volume in cubic yards - this calculator converts your slab's dimensions directly into an order-ready figure.

Formula

Volume (cu ft) = Length x Width x (Thickness in inches / 12)
Volume (cu yd) = Volume (cu ft) / 27, then apply a 5% waste factor

Example

A 20 ft x 10 ft slab, 4 inches thick:

Volume = 20 x 10 x (4/12) = 66.67 cu ft = 2.47 cu yd → 2.59 cu yd with waste allowance

Why the 5% Waste Buffer?

This accounts for minor over-excavation, spillage during pouring, and slight thickness variation across the slab (few slabs are perfectly uniform in depth) - concrete that sets before it's placed can't be salvaged, so slightly overordering is far cheaper than running short mid-pour and needing a rushed second delivery.

Watch for Minimum Order Quantities

Most ready-mix concrete suppliers have a minimum order quantity (often several cubic yards) - very small slabs may end up paying for more concrete than this calculation suggests, simply due to the supplier's delivery minimum, regardless of the actual calculated volume needed.