Concrete Calculator

Estimate concrete volume for rectangular slabs, footings or walls, and circular columns. Calculate cubic yards, cubic meters, and bag counts with editable yield and waste percentage.

Formula

Volume = area × depth (or length × width × depth). Bags = ceil(volume after waste ÷ bag yield). 1 cubic yard = 27 cubic feet.

Assumptions

Bag yield is user-editable because product coverage varies by mix and manufacturer.
Waste percentage is an estimate for ordering — not a structural safety factor.

Limitations

Does not provide structural engineering recommendations.
Actual use varies with subgrade, spillage, and settling.

Worked example

10 ft × 10 ft slab, 4 in thick

Volume = 33.33 cu ft ≈ 1.23 cu yd. At 10% waste and 0.6 cu ft per bag, about 61 bags.

Frequently asked questions

How many bags do I need?

Enter the stated yield per bag in cubic feet (common 80 lb bags are often about 0.6 cu ft). Bag counts are rounded up to avoid running short.

Should I add extra concrete?

A waste percentage accounts for spillage, uneven excavation, and subgrade variation. Structural projects require qualified professional review.

Last reviewed: 2026-07-23

Category: Construction & Materials

Results are provided for informational purposes only and may not reflect real-world policies, fees, or individual circumstances.