Concrete Calculator
Free online Concrete Calculator.
Calculator
How to Use
- Enter the required values
- Click Calculate to see the result
- Review the detailed output
Formula
Volume = Length x Width x Depth (in consistent units). Cubic yards = cubic feet / 27. Add 5-10% for waste. Bags needed = total volume / yield per bag.
Example Calculations
Patio Slab
Input: 20ft x 15ft x 4 inches thick
Result: 3.70 cubic yards, ~93 bags (80lb each)
Footing
Input: 50ft length x 2ft wide x 1ft deep
Result: 3.70 cubic yards of concrete
Post Holes
Input: 10 holes, 12in diameter, 36in deep
Result: Total: 1.96 cubic yards
About This Calculator
Free online concrete calculator. Calculate instantly in your browser with our easy-to-use tool. No sign-up required.
Our concrete calculator is free, easy to use, and provides instant results. All calculations are performed in your browser for privacy and speed.
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Frequently Asked Questions
How much concrete do I need?
Multiply length x width x depth in same units. Convert cubic feet to cubic yards by dividing by 27. Add 5-10% for waste.
How many bags of concrete?
80-lb bag yields ~0.6 cu ft, 60-lb yields ~0.45 cu ft. Divide total needed by yield per bag, add 10%.
Standard concrete mix ratio?
1 part cement, 2 parts sand, 3 parts aggregate with water at 0.4-0.6x cement volume. This 1:2:3 ratio works for most projects.
How thick should a slab be?
4 inches for patios/walkways, 6 inches for driveways. Heavy loads may need 6-8 inches.
Does rebar affect volume?
Rebar displacement is negligible for residential projects. Focus on accurate slab dimensions.