Concrete Calculator – Slabs & Footings
Free concrete calculator: estimate volume in cubic feet and cubic yards, and the number of 60lb or 80lb bags for slabs and footings. No sign-up.
Concrete Calculator
Estimate concrete volume for slabs or footings. Enter dimensions in feet. Results show volume and approximate bag counts (60 lb and 80 lb).
How the concrete calculator works
Volume (cubic feet) = length × width × depth
Cubic yards = cubic feet ÷ 27
Bag estimates use typical yields: ~45 bags per cubic yard for 80lb, ~60 for 60lb. Add extra for waste. For cement in custom mixes, use the cement calculator.
Estimating concrete for your project
Concrete is sold by volume (cubic yards) or by bag. For a rectangular slab or footing, volume is length × width × depth. A 10 ft × 10 ft × 4 in slab is 10 × 10 × (4/12) = 33.3 cubic feet, or about 1.23 cubic yards. Ordering slightly more (e.g. 1.5 cubic yards) accounts for spillage, uneven subgrade, and rounding by suppliers.
Bagged concrete is convenient for small projects. A typical 80lb bag yields about 0.6 cubic feet when mixed. For 33.3 cubic feet, you would need roughly 56 bags. The calculator rounds up to ensure you have enough. Store bags in a dry place and mix only what you can place within the working time.
For footings, measure the length, width and depth of each section. Add the volumes if you have multiple footings. Frost depth and local codes affect required depth; consult your building department. For complex shapes, break the area into rectangles and sum the volumes.
This calculator provides estimates only. Actual yields vary by mix, water content, and placement. For large pours, ready-mix suppliers will calculate quantities from your dimensions. Use our cement calculator if you are mixing your own concrete from cement, sand and aggregate.