What it calculates
Calculate cubic yards and bag quantities for slabs and footings.
Concrete Calculator
Estimate cubic yards and bag quantities for a slab, footing or rectangular pour.
Planning and estimating aid only. Verify project requirements, manufacturer instructions, adopted codes, permits, and field conditions before performing regulated work.
Construction estimating
How to Use This Calculator
Enter the measurements and job information you know, select Calculate, then use the result as a starting point for estimating, purchasing or project planning.
How the calculation works
Length × width × depth gives cubic feet. Cubic feet are divided by 27 for cubic yards and the waste factor is added.
What the result means
Order quantity should also consider subgrade variation, over-excavation and supplier minimums.
A 12 × 10-foot slab example
At 4 inches thick, a 12 × 10-foot rectangular slab has 40 cubic feet of volume: 12 × 10 × (4 ÷ 12). Divide by 27 for 1.48 cubic yards. A 10% allowance gives about 1.63 cubic yards. At the tool’s assumed 0.6 cubic feet per 80-lb bag, that is 74 bags rounded up.
Contractor tip: Depth is entered in inches while length and width are feet. Convert depth once. Thickened edges, steps and footings need their own measured volumes.
Verify the final quantity
The bag estimate uses an assumed yield. Read the actual product yield and check delivery increments. This volume calculation does not specify slab design, strength, reinforcement, footing dimensions or subgrade preparation.
Good practice: Compare the calculated quantity with plans, specifications, product packaging and current field conditions before purchasing material.