How to calculate concrete
- Work out the volume. Length × width × thickness in feet gives cubic feet; ÷ 27 for cubic yards.
- Multiply by the weight per volume. Normal concrete is about 2,400 kg per cubic metre, or about 1,837 kg per cubic yard.
- Convert to tonnes. Divide kilograms by 1,000.
- Check the load. Compare with what your trailer, truck or floor is rated for.
Worked example: a 12 × 20 ft patio, 4 inches thick
- Volume: 12 × 20 × (4 ÷ 12) = 80.0 cu ft, 2.96 yd³ or 2.27 m³.
- Weight: 80.0 cu ft × 150 lb = 12,000 lb, that is 5,443 kg, about 5.4 tonnes.
- The calculator adds your waste percentage to the volume, so its weight is a little higher.
Concrete weight by volume
| Cubic yards | Cubic metres | Kilograms | Tonnes |
|---|---|---|---|
| 0.25 | 0.19 | 459 | 0.5 |
| 0.50 | 0.38 | 919 | 0.9 |
| 1.00 | 0.76 | 1,837 | 1.8 |
| 2.00 | 1.53 | 3,674 | 3.7 |
| 3.00 | 2.29 | 5,511 | 5.5 |
| 5.00 | 3.82 | 9,185 | 9.2 |
| 10.00 | 7.65 | 18,370 | 18.4 |
Normal concrete at 2,403 kg per m³ (150 lb per cu ft).
Weight of a concrete slab
| Thickness | kg per sq ft | lb per sq ft | 10 × 10 ft slab (kg) |
|---|---|---|---|
| 3 in | 17.0 | 37.5 | 1,701 |
| 4 in | 22.7 | 50.0 | 2,268 |
| 5 in | 28.3 | 62.5 | 2,835 |
| 6 in | 34.0 | 75.0 | 3,402 |
| 8 in | 45.4 | 100.0 | 4,536 |
Normal concrete at 2,403 kg per m³.
Concrete formulas by shape
All measurements in feet; divide inches by 12 first. Results are in cubic feet.
- Slab
- length × width × thickness
- Round slab
- π × (diameter ÷ 2)² × thickness
- Continuous footing
- total length × width × depth
- Pad footing
- length × width × depth × number of footings
- Monolithic slab
- length × width × thickness + perimeter band × (edge depth − thickness), where perimeter band = length × width − (length − 2 × edge width) × (width − 2 × edge width)
- Bell footing
- π × r² × pier height + π × bell height ÷ 3 × (R² + R × r + r²), with r = pier radius and R = bell radius
- Wall
- length × height × thickness
- Column / pier
- π × (diameter ÷ 2)² × height
- Post hole
- (hole area − post area) × depth; round hole π × (diameter ÷ 2)², square hole width²
- Tube / ring
- π × [(outer ÷ 2)² − (inner ÷ 2)²] × height
- Curb & gutter
- [curb depth × (curb height + flag thickness) + gutter width × flag thickness] × length
- Steps (solid, n steps)
- width × rise × run × (1 + 2 + … + n). With a landing, the landing is the top step: width × rise × [run × (1 + … + (n − 1)) + landing depth × n]
Cubic yards = cubic feet ÷ 27. Cubic metres = cubic feet ÷ 35.31.
Frequently asked questions
How much does a cubic metre of concrete weigh?
About 2,400 kg, or 2.4 tonnes. We use 2,403 kg (150 lb per cubic foot), the same figure as the calculator.
How much does a cubic yard of concrete weigh?
About 1,837 kg, or 4,050 lb: a little less than a cubic metre, since a yard is 0.76 m³.
How much does a 4 inch slab weigh per square foot?
About 22.7 kg (50 lb) per square foot; 34.0 kg at 6 inches.
Does reinforced concrete weigh more?
A little: with rebar it is often taken as about 2,500 kg per cubic metre. Lightweight concrete is much lighter, roughly 1,400 to 1,850 kg.
About the prices
Costs are estimated ranges with source and date, never a quote. Enter your local prices under "Use your own prices", or read how we estimate prices.