Free online concrete calculator

How to use

1. Choose your shape: Slab, Footing, or Column.
2. Pick Imperial (feet and inches) or Metric (meters).
3. Enter dimensions — length, width, and depth for slabs/footings; radius and height for columns.
4. Set the count if you’re pouring multiple identical elements.
5. Read cubic yards, cubic feet, cubic meters, and bag counts in the results.

Formulas

Rectangular slab or footing (imperial):

cubic feet = length (ft) × width (ft) × depth (in) ÷ 12
cubic yards = cubic feet ÷ 27

Cylindrical column (imperial):

cubic feet = π × (radius in ÷ 12)² × height (ft)
cubic yards = cubic feet ÷ 27

Metric (all dimensions in meters):

cubic meters = length × width × depth   (slab/footing)
cubic meters = π × radius² × height     (column)

Bag counts:

60-lb bags = ceil(cubic feet ÷ 0.45)
80-lb bags = ceil(cubic feet ÷ 0.60)

Unit conversions

Worked example

Driveway slab: 20 ft × 10 ft × 4 in deep

cubic feet  = 20 × 10 × (4 ÷ 12) = 66.67 ft³
cubic yards = 66.67 ÷ 27         = 2.47 yd³
60-lb bags  = ceil(66.67 ÷ 0.45) = 149 bags
80-lb bags  = ceil(66.67 ÷ 0.60) = 112 bags

Order 2.5 cubic yards of ready-mix (always round up slightly when ordering) or 112 bags of 80-lb concrete mix.

Notes

• Always add 5–10% extra when ordering ready-mix to account for spillage and uneven sub-grade.
• Bag yield varies slightly by brand; the calculator uses the standard 0.45 ft³ for 60-lb and 0.60 ft³ for 80-lb.
• For large pours (>1 yd³), ready-mix is usually more cost-effective and consistent than bags.