How the cement calculator works
Concrete
The wet volume of concrete is length × width × depth. Dry ingredients occupy more space before water is added, so the dry volume is taken as 1.54 × wet volume — the standard allowance for voids, bulking and site losses. The dry volume is then split in the mix ratio:
Cement (m³) = dry volume × cement part ÷ (sum of parts)
Cement (kg) = cement volume × 1,440 kg/m³ · Bags = kg ÷ 50
Example — 1 m³ of M20 (1 : 1.5 : 3): dry volume 1.54 m³ → cement 1.54 ÷ 5.5 = 0.28 m³ → 403 kg → about 8.1 bags, with 0.42 m³ sand and 0.84 m³ aggregate.
Plaster
Wet mortar volume is area × thickness. The dry volume is taken as 1.27 × wet volume, then split in the cement : sand ratio. For 100 m² of 12 mm plaster in 1 : 4 mortar, that works out to about 8.8 bags of cement.
Cement required per cubic metre of concrete
| Grade | Nominal mix | Cement (kg/m³) | Bags per m³ | Sand (m³) | Aggregate (m³) |
|---|---|---|---|---|---|
| M5 | 1:5:10 | 139 | 2.8 | 0.48 | 0.96 |
| M7.5 | 1:4:8 | 171 | 3.4 | 0.47 | 0.95 |
| M10 | 1:3:6 | 222 | 4.4 | 0.46 | 0.92 |
| M15 | 1:2:4 | 317 | 6.3 | 0.44 | 0.88 |
| M20 | 1:1.5:3 | 403 | 8.1 | 0.42 | 0.84 |
| M25* | 1:1:2 | 554 | 11.1 | 0.39 | 0.77 |
*IS 456 permits nominal mixes up to M20. M25 and above should be design mixes as per IS 10262 — the M25 row is an estimate only.
Which cement should you use?
- RCC columns, beams, slabs: OPC 53 or OPC 43; PPC for slabs where early strength is not critical.
- Plaster and brickwork: PPC for workability and finish.
- Foundations in saline or coastal soil: PSC.
Still deciding? Read OPC vs PPC — the complete guide.