Round Slab Concrete Calculator
For a circular patio or equipment pad, measure the finished diameter at its widest point and use the planned thickness.
How the calculation works
Volume in cubic feet = π × (diameter in feet ÷ 2)² × (thickness in inches ÷ 12). Divide by 27 for cubic yards. The waste allowance applies after exact volume is calculated.
Worked example
A 12 ft diameter slab at 4 in thick contains about 37.70 ft³, or 1.40 yd³. With 10% extra, the order estimate is 1.54 yd³, equivalent to 70 bags at 0.60 ft³ yield.
Before you order
A circular edge, thickened perimeter or uneven base changes the amount. Measure the finished depth at several points. Thickness and reinforcement are design decisions outside this quantity estimate.
Review the calculation method and source notes, then use the supplier checklist before placing an order.
Continue planning
Content and calculator by pourmeasure. Formula and assumption notes: methodology and sources. Updated October 2026. No independent engineering review is claimed.