Concrete Calculator

Concrete is a mix of cement, sand and aggregate (gitti) with water. The grade tells you the mix: M20, for example, is 1 part cement, 1.5 parts sand and 3 parts aggregate. This calculator works out how much of each you need for a slab, floor, footing or beam.

How to use the concrete calculator

1. Enter the length and width in feet.
2. Enter the thickness in inches (for example, 5 inches for a roof slab or 3 to 4 inches for a floor).
3. Choose the grade.

For a beam or column, enter its length, width and depth the same way.

How it is calculated

Wet volume = length × width × thickness
Dry volume = wet volume × 1.54
Cement     = dry volume × cement part ÷ total parts   (1 m³ cement = 28.8 bags of 50 kg)
Sand       = dry volume × sand part ÷ total parts
Aggregate  = dry volume × aggregate part ÷ total parts
Water      = cement weight × 0.5

Example

A roof slab 10 ft × 10 ft, 5 inches thick, in M20:

• Concrete volume: 10 × 10 × 5/12 = 41.7 cft (1.18 m³)
• Cement: about 9.5 bags
• Sand: about 17.5 cft
• Aggregate: about 35 cft
• Water: about 238 litres

Important

• These are nominal mixes. For M25 and stronger, and for any structural work, the Indian standard IS 456 recommends a design mix from an engineer.
• The 1.54 factor covers voids and shrinkage. Add 2 to 5% for wastage at site.
• Cure the concrete by keeping it wet for at least 7 days, and longer for slabs, to reach full strength.