The formula
For length and width in feet and thickness in inches: cubic yards = length × width × (thickness ÷ 12) ÷ 27. If every measurement is in inches, divide length × width × thickness by 46,656.
Worked example: 10 feet by 10 feet by 4 inches
The slab volume is 10 × 10 × (4 ÷ 12) ÷ 27 = approximately 1.235 cubic yards. A 5% allowance gives approximately 1.30 cubic yards; a 10% allowance gives approximately 1.36 cubic yards. These are planning estimates, not order guarantees.
Measure separate sections
Break an irregular layout into shapes that you can measure. Calculate each rectangular section and add the results. Footings, thickened edges and deeper sections need their own volume; a single slab thickness will not account for them.
Choose an allowance deliberately
Uneven subgrade, form variations and placement losses can change actual usage. Our calculator separates the measured volume from your optional allowance. Agree on final yardage with the project team rather than assuming a percentage fits every site.
Common questions
Can I enter inches instead of feet?
Yes. Choose the length and width units in the calculator. Thickness is always entered in inches.
Does the calculator quote a price?
No. Send the estimated volume with the job location and mix requirements to request a delivery quote.