Concrete Volume Calculator
Whether you're pouring a driveway slab, setting fence posts, or casting cylindrical columns, knowing the correct concrete volume prevents under-ordering (leaving a pour short) or over-ordering (wasted material and cost). This calculator handles rectangular slabs and circular cylinders, converts the result to cubic yards for ordering, and estimates how many pre-mixed bags you'll need for small pours.
Calculator
Formula
Formula
Slab: V = L × W × D Cylinder: V = π × (d/2)² × h
For a rectangular slab: V = Length × Width × Depth. For a cylinder: V = π × r² × h, where r is the radius (diameter ÷ 2) and h is the height. Depth is entered in inches and converted to feet (÷ 12) internally. 1 cubic yard = 27 cubic feet. The bag estimate adds a 10% waste factor and rounds up to a whole number of bags.
Worked example
A rectangular patio slab 12 ft × 10 ft, 4 inches deep. How many 80 lb bags are needed?
- 1.Convert depth: 4 in ÷ 12 = 0.333 ft
- 2.V = 12 ft × 10 ft × 0.333 ft = 40.0 ft³
- 3.V in yd³ = 40.0 ÷ 27 = 1.481 yd³
- 4.V in m³ = 40.0 × 0.0283168 = 1.133 m³
- 5.An 80 lb bag covers 0.60 ft³ → 40.0 / 0.60 = 66.7 bags
- 6.With 10% waste: 66.7 × 1.10 = 73.4 → round up to 74 bags
1.48 cubic yards of concrete. Order 74 × 80 lb bags, or about 1.65 yd³ ready-mix (includes waste).
Assumptions and limitations
- For cylinders, the 'Length' input is treated as diameter.
- Depth is entered in inches; all other dimensions in feet.
- Bag yield: 40 lb = 0.30 ft³, 60 lb = 0.45 ft³, 80 lb = 0.60 ft³ (Quikrete standard yield).
- A 10% waste factor is applied to the bag estimate. For ready-mix orders, 5–10% is typical.
- Does not account for rebar, forms, or sub-base material.
- For multiple sections (e.g., multiple footings), calculate each separately and sum.
Frequently asked questions
Related tools and guides
Convert cubic feet, cubic yards, cubic meters, and liters.
Convert feet to meters, inches to centimeters.
Quick feet → meters reference.
Why construction in the US uses feet and yards while metric is standard elsewhere.