How to Calculate Concrete Volume for a Slab

To estimate concrete for a rectangular slab, multiply the slab length by its width and thickness. Keep all three dimensions in compatible units.

How to calculate it

1. Measure the slab length and width.
2. Measure the slab thickness.
3. Multiply length × width × thickness to get the required volume.
4. Add an allowance for waste or uneven conditions when you turn the estimate into a purchasing quantity.

Formula

Concrete volume = length × width × thickness.

Example

For a 20 ft × 10 ft slab that is 0.5 ft thick, the calculation is 20 × 10 × 0.5 = 100 cubic feet.

Important notes

• Do not mix feet and inches without converting them first.
• The calculator gives a geometric estimate. Actual orders can depend on site conditions, forms, slopes and supplier requirements.
• For bagged concrete, use the concrete bag calculator after determining the required volume.

Before ordering materials

Use measurements from the actual project whenever possible and keep all dimensions in compatible units. Material coverage, yield, density, package size, waste, compaction, cuts, overlaps, and site conditions can affect the quantity that must be purchased.

The calculation on this page is intended as a transparent estimating method. Compare the result with manufacturer instructions, supplier ordering units, project drawings, and applicable local requirements before placing an order.

Use the How to Calculate Concrete Volume for a Slab calculator

This page provides a practical estimating method. Verify project specifications, local requirements and manufacturer instructions before purchasing materials.