Concrete Volume
Calculate concrete in cubic yards and bags for a slab.
About Concrete Volume
A slab's volume is length times width times thickness converted to cubic yards. Adding an overrun allowance and converting to eighty-pound bags approximates the material needed. Ready-mix concrete is ordered in cubic yards, and an overrun buffer prevents running short mid-pour.
Formula
Concrete Volume
Cubic yards = length x width x thickness / 12 / 27
- overrun
- Buffer for uneven ground and spillage
Worked example
With the default values below, Concrete Volume returns Concrete Needed of 1.6. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Slab length
- 12 ft
- Slab width
- 10 ft
- Slab thickness
- 4 in
- Overrun allowanceaccepts 0–25 %
- 5 %
Results
- Volume
- 42.0 cu ft
- Concrete Needed
- 1.6 cu yd
- 80 lb Bags
- 70 bags
Step by step
- 1Values used
- 2Concrete Volume
- 3Concrete Needed= 1.6 cu yd
- 4Volume= 42.0 cu ft
- 580 lb Bags= 70 bags
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Concrete Volume calculated?
Cubic yards = length x width x thickness / 12 / 27 A slab's volume is length times width times thickness converted to cubic yards. Adding an overrun allowance and converting to eighty-pound bags approximates the material needed.
Why does Concrete Volume matter?
Ready-mix concrete is ordered in cubic yards, and an overrun buffer prevents running short mid-pour.
What values do I need to enter?
This calculator takes 4 inputs: Slab length, Slab width, Slab thickness, Overrun allowance. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.