How to estimate concrete for a rectangular slab
For a rectangular slab, volume is footprint area multiplied by slab thickness. The important practical step is keeping the engineering/design decision about thickness separate from the arithmetic. Enter the dimensions your project actually requires, then use the calculator to convert them into a material quantity.
Thickness drives volume quickly
Changing slab thickness changes volume in direct proportion. Moving from 4 inches to 5 inches increases concrete volume by 25% for the same footprint.
Raw volume versus order quantity
The raw mathematical volume assumes exact dimensions. The order quantity can include an editable allowance for uneven subgrade, form variation or incidental loss.
Structural slabs need more than a quantity calculator
Reinforcement, edges, footings, frost conditions, loads and local code are project-specific. Use this page to estimate volume, not to determine structural design.
The slab contains about 5.93 yd³ of concrete before allowance. A 10% planning allowance brings that to about 6.52 yd³.