Construction estimator
Concrete Calculator
Enter the size of the slab, footing or column and pick the concrete grade to estimate cement bags, sand and aggregate. Your entered values stay out of analytics.
Formula and assumptions
Wet volume = length × width × thickness. Order volume = wet volume × (1 + wastage). Dry volume = order volume × 1.54. Each material = dry volume × its share of the mix ratio. Cement bags = cement volume × 1,440 kg/m³ ÷ 50 kg, rounded up to buy.
- Nominal mix by volume (cement : sand : coarse aggregate) for the chosen grade.
- Dry volume is 1.54 times the wet volume, the usual factor for shrinkage and voids.
- Bulk densities: cement 1,440 kg/m³, sand 1,600 kg/m³, coarse aggregate 1,500 kg/m³. Cement is bought in 50 kg bags.
- Wastage is added to the wet volume before the dry volume is worked out.
- An estimate for buying materials. It does not cover steel, shuttering, water, admixtures, sand bulking or structural design.
- Volumes and masses are shown to 2 decimal places. Cement bags to buy are rounded up to a whole bag; sand and aggregate are not rounded to loads.
Formula version 1.0, last reviewed Reviewed by an external trade reviewer, 6 October 2026; released by the owner.
Frequently asked questions
Why is the dry volume 1.54 times the wet volume?
Dry cement, sand and aggregate pack together and lose volume once water is added, so more dry material is needed than the finished concrete. Sites use between 1.52 and 1.57; this tool uses 1.54.
Which grades are nominal mixes?
M5 to M20 are the nominal mixes offered here. M25 and above are not offered, because structural concrete at those grades needs a specified or design mix. The traditional 1 : 1 : 2 ratio can be entered as a custom ratio in the Cement-Sand-Aggregate Calculator, without any claim that it produces M25 concrete.
What does this not include?
Reinforcement steel, shuttering, water, admixtures, sand bulking from moisture and any structural design. It is an estimate for buying materials, not an engineering check.
Why are the bags rounded up?
Cement is sold in whole bags, so the amount to buy is the exact figure rounded up. The exact figure is shown too.