Concrete Calculator
Estimate concrete for slabs, footings, walls, and columns with waste and bag counts
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How Concrete Volume Is Estimated
Each shape uses a simple volume formula, then applies your waste allowance.
Shape formulas
Slabs and footings use rectangular volume formulas. Walls use length by height by thickness. Columns use pi times radius squared times height.
Waste allowance
Concrete projects commonly include extra material for uneven subgrade, form variation, spillage, and finishing. Adjust the waste percentage to match the job.
Bags vs ready-mix
Small jobs can be planned by bag count. Larger pours are usually ordered in cubic yards or cubic meters from a ready-mix supplier.
Concrete Examples
Quick reference estimates for common small concrete projects.
Concrete Calculator FAQ
Practical answers for estimating pours, waste, bag counts, and unit conversions.
How much extra concrete should I order?
A 5% to 10% waste allowance is common for many pours. Use a higher allowance for uneven excavation, complex forms, small pours, or situations where running short would delay the project.
How do I calculate concrete for a slab?
Multiply length by width by thickness. In imperial measurements, convert thickness from inches to feet first, then divide cubic feet by 27 to get cubic yards.
Should I use bagged concrete or ready-mix?
Bagged concrete works well for small repairs and posts. Ready-mix is usually better for larger slabs, footings, and walls because it reduces labor and improves consistency.
Why are bag counts only estimates?
Bag yield varies by product, water amount, compaction, waste, and site conditions. Always compare the calculator estimate with the yield printed on the bags you plan to buy.
Can I calculate concrete in metric units?
Yes. Switch to metric mode to enter dimensions in meters or centimeters and see the primary volume in cubic meters, with supporting conversions for planning.