Concrete Calculator
Estimate concrete in cubic yards and bags for slabs, footings, columns and steps with one shape engine.
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What this tool does
Estimate concrete in cubic yards and bags for slabs, footings, columns and steps with one shape engine. Steps are modelled as stacked solid boxes (each step a full-height block), the standard estimating method. Bag yields are typical manufacturer values — verify the bag label. Reinforcement and structural design are not included.
How to use the Concrete Calculator
- Enter or select shape.
- Enter or select length in ft.
- Enter or select width in ft.
- Enter or select slab / footing thickness in in.
- Enter or select column diameter in in.
- Enter or select column height in ft.
- Enter or select number of pieces (columns / footings).
- Enter or select number of steps.
- Enter or select step rise in in.
- Enter or select step run (tread depth) in in.
- Enter or select step width in ft.
- Enter or select waste allowance (%).
- Enter or select bag weight.
- Read the calculated result; change any measurement to compare alternatives.
Formula
slab: L×W×depth/12; column: π×(diameter/24)²×height×count; steps: width×run×rise/144×n(n+1)/2; yd³ = cu ft/27 with waste; bags = ceil(cu ft / bag yield)
- shape
- Shape
- length
- Length (ft, before metric conversion)
- width
- Width (ft, before metric conversion)
- depth
- Slab / footing thickness (in, before metric conversion)
- diameter
- Column diameter (in, before metric conversion)
- colHeight
- Column height (ft, before metric conversion)
- count
- Number of pieces (columns / footings)
- stepCount
- Number of steps
- stepRise
- Step rise (in, before metric conversion)
- stepRun
- Step run (tread depth) (in, before metric conversion)
- stepWidth
- Step width (ft, before metric conversion)
- waste
- Waste allowance (%)
- bag
- Bag weight
Steps are modelled as stacked solid boxes (each step a full-height block), the standard estimating method. Bag yields are typical manufacturer values — verify the bag label. Reinforcement and structural design are not included.
Worked example
For concrete calculator, the following measurements illustrate the exact method: Shape: slab; Length: 20; Width: 10; Slab / footing thickness: 4; Column diameter: 12; Column height: 8; Number of pieces (columns / footings): 1; Number of steps: 4; Step rise: 7; Step run (tread depth): 11; Step width: 4; Waste allowance (%): 10; Bag weight: 0.3.
Inputs
- ShapeSlab / footing (rectangle)
- Length20 ft
- Width10 ft
- Slab / footing thickness4 in
- Column diameter12 in
- Column height8 ft
- Number of pieces (columns / footings)1
- Number of steps4
- Step rise7 in
- Step run (tread depth)11 in
- Step width4 ft
- Waste allowance (%)10
- Bag weight40 lb (0.3 cu ft yield)
Result
- Concrete volume2.72 cu yd
- Volume in cubic feet73.33 cu ft
- Bags to buy245
- Ready-mix loads (8 yd³ truck)0.4
Typical concrete bag yield
| Bag weight (lb) | Yield (cu ft) |
|---|---|
| 40 | 0.3 |
| 60 | 0.45 |
| 80 | 0.6 |
Results explained
- Concrete volume
- Concrete volume from the formula above, expressed in yd3 before metric conversion. Steps are modelled as stacked solid boxes (each step a full-height block), the standard estimating method. Bag yields are typical manufacturer values — verify the bag label. Reinforcement and structural design are not included.
- Volume in cubic feet
- Volume in cubic feet from the formula above, expressed in cuft before metric conversion. Steps are modelled as stacked solid boxes (each step a full-height block), the standard estimating method. Bag yields are typical manufacturer values — verify the bag label. Reinforcement and structural design are not included.
- Bags to buy
- Bags to buy from the formula above. Steps are modelled as stacked solid boxes (each step a full-height block), the standard estimating method. Bag yields are typical manufacturer values — verify the bag label. Reinforcement and structural design are not included.
- Ready-mix loads (8 yd³ truck)
- Ready-mix loads (8 yd³ truck) from the formula above. Steps are modelled as stacked solid boxes (each step a full-height block), the standard estimating method. Bag yields are typical manufacturer values — verify the bag label. Reinforcement and structural design are not included.
Frequently asked questions
At 4 in thick, 10 × 10 ft is 33.3 cu ft = 1.23 yd³ before waste. Choose the slab shape, enter 10 × 10 ft and 4 in, and set waste to 0 to reproduce it; add 10% waste for ordering.
A cubic yard is 27 cu ft: about 45 bags of 80 lb (0.6 cu ft each), 60 bags of 60 lb, or 90 bags of 40 lb. Past roughly 1 yd³, ready-mix is usually cheaper and far less work.
Each step is treated as a solid block as tall as its position in the flight, so total volume = width × run × rise × n(n+1)/2. That matches how estimators price poured steps, including the solid fill under the treads.
π × (diameter/24)² × height in feet. A 12 in diameter, 8 ft column is about 6.3 cu ft — roughly 11 bags of 80 lb mix.
Yes — 5–10% waste covers uneven subgrade, spillage and forms that bow. Short loads are expensive; a little extra is cheap insurance.
It generalises them: slab, footing, bag and column math all live here. The older tools remain for their single-purpose pages.