What is it?
The Concrete Calculator tells you how much concrete a slab, footing or floor needs. It shows the volume in cubic metres and cubic feet, and the cement bags, sand and gravel for the mix you choose.
Who is it for?
Homeowners building or repairing, contractors and masons estimating materials, and civil engineering students.
How to use it
Enter Length, Width and Thickness, and choose the Mix (cement : sand : aggregate). The answer appears as you type; there is no Calculate button. Tap Copy result to copy it, or Share on WhatsApp to send it.
Which mix?
- 1:1.5:3 (M20): RCC slabs, beams and columns in houses.
- 1:2:4 (M15): footpaths, floors, lighter work.
- 1:3:6 or 1:4:8: PCC base under footings and floors.
How it is worked out
It uses a nominal mix with the usual 1.54 dry-volume factor; one 50 kg bag is about 0.0347 m³. Add 5–10% for wastage. Dry materials shrink when water is added, which is why the dry volume is more than the wet concrete.
Common mistakes
- Thickness in the wrong unit: a 5-inch slab is 0.127 m, not 5 m.
- Forgetting beams and drops under the slab.
- For structural work follow your engineer’s design mix; ready-mix concrete is ordered by grade (M20, M25) and volume.
These are estimates for planning and buying. For structural work, follow your engineer’s or contractor’s quantities.
Errors and how to fix them
- A result shows a dash (—): a box is empty or has something that is not a number in it, such as a comma or a letter. Type plain digits; use a dot for decimals.
- The amount looks 100 times too big: Length, Width and Thickness are all in metres. A 6-inch (15 cm) slab is 0.15, not 15.
- Cement bags don’t match the contractor’s figure: different mixes and wastage allowances give different numbers. Compare using the same Mix (cement : sand : aggregate).
Open the tool: Concrete Calculator
Still stuck?
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Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.