Rectangle Concrete Calculator
The rectangle is the workhorse of concrete work — slabs, pads, walks and floors. This rectangle concrete calculator multiplies length × width × thickness and converts to every ordering unit.
How to Use This Calculator
- Enter your dimensions — feet for lengths, inches for thickness.
- Adjust the options — waste percentage, bag size and your local concrete price.
- Read your results — volume, bags, weight and cost update live as you type.
The Formula
Rectangle volume = Length × Width × Thickness Worked example: A 12 × 10 ft pad at 4 in: 12 × 10 × 0.333 = 40 ft³ ÷ 27 ≈ 1.48 yd³ (≈ 1.13 m³).
Every concrete calculator rectangle computation reduces to three numbers, but unit slips cause most ordering errors — thickness measured in inches must become feet (divide by 12) before multiplying.
Rectangles also underpin composite estimates: L-shapes, U-shapes and stepped slabs are just rectangles added together. If your pour is several rectangles, run each here and sum, or use the irregular shape calculator.
Results include cubic feet, cubic yards, cubic meters and litres, plus bags by size, concrete weight and cost with your local price.
Frequently Asked Questions
Common questions about the rectangle concrete calculator.
How do I calculate concrete for a rectangle?
Length × width × thickness in one unit. In feet: a 20 × 10 ft slab at 4 in is 20 × 10 × 0.333 = 66.7 ft³ ≈ 2.47 yd³.
Does it work in metric?
Yes — switch to metric and enter meters and centimeters; results show cubic meters and litres alongside imperial units.
What about non-rectangular pours?
Use the dedicated circle, triangle, trapezoid, octagon or L-shape calculators, or split any odd footprint into rectangles with the irregular shape calculator.
How much waste should I add?
5% for clean formed rectangles, 10% for pours on rough or sloping subgrade.
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