Cement Calculator — Bags of Cement Required
Work out how many 50 kg cement bags, and how much sand and aggregate, a concrete pour needs. Enter the wet volume of concrete and the nominal mix you are using.
Inputs
- Wet volume of concrete (cubic metres)
- Cement part of mix (parts)
- Sand part of mix (parts)
- Aggregate part of mix (parts)
How this calculation works
- Dry volume = wet volume × 1.54 (concrete shrinks when mixed)
- Cement volume = dry volume × (cement part ÷ total parts)
- Cement bags = cement volume × 1440 kg/m³ ÷ 50 kg per bag
- Sand and aggregate volume = dry volume × their share of the mix
Example: For 10 m³ of M20 concrete (1 : 1.5 : 3), dry volume is 15.4 m³. Cement share is 1/5.5 = 2.8 m³, which is 2.8 × 1440 ÷ 50 ≈ 81 bags, with about 4.2 m³ sand and 8.4 m³ aggregate.
Frequently asked questions
How many cement bags are in 1 cubic metre of M20 concrete?
About 8.1 bags of 50 kg cement per cubic metre of M20 (1 : 1.5 : 3) concrete, along with roughly 0.42 m³ of sand and 0.84 m³ of aggregate.
Why multiply the wet volume by 1.54?
Dry materials lose volume when water is added and the mix compacts. The 1.54 factor converts the finished (wet) concrete volume back into the dry material volume you have to buy.
Does this include wastage?
No. Site wastage is usually 3 to 5 percent, so add that on top of the calculated quantity when ordering.