Slab 1
Length: — ft · Width: — ft · Thickness: — in
Slab and patio planner
Concrete Slab Calculator
Calculate concrete for rectangular, round, L-shaped, and thickened-edge slabs without hiding waste or rounding.
Project
Formula
How the result is calculated
Rectangular slab volume = length × width × thickness. Thickness is converted from inches to feet before cubic feet are divided by 27.
Worked example
Check the order logic
A 20 × 20 ft slab at 4 in thick is 4.94 yd³ before waste. The order quantity becomes 5.50 yd³ with the default allowance and rounding.
Assumptions
Waste and supplier rounding stay editable
The launch defaults are 10% waste and upward rounding to 0.25 yd³ or 0.10 m³. Open “Adjust assumptions and costs” to use your supplier’s increment, actual prices, density, truck capacity, or product bag yield.
Questions
What this calculator does
Which slab shapes are supported?
Rectangle, circle, L-shape, and a thickened-edge estimate.
Why is the order number higher than the calculated volume?
The result shows waste and supplier rounding as separate additions.
Does the calculator decide slab thickness?
No. Enter the thickness required for your project and local conditions.
Related tools
Continue planning
Concrete bag calculator · Ready-mix vs. bags · Concrete cost calculator
Bag yields follow the cited manufacturer data. See sources and review dates.