Plaster quantity calculation: cement and sand for cement plaster
To estimate cement and sand for plaster, find the wet volume of mortar (area × thickness), convert it to a dry volume, and split that in the ratio of the mix. For 100 m² of 12 mm plaster in cement mortar 1:6 that gives about 6.3 bags of cement and 1.31 m³ of sand.
Step 1 — Wet volume of mortar
Wet volume = area × thickness = 100 m² × 0.012 m = 1.20 m³.
Step 2 — Dry volume
Dry cement and sand shrink when water is added, and some mortar fills the joints and hollows of the wall. The usual allowance multiplies the wet volume by 1.27:
Dry volume = 1.20 × 1.27 = 1.524 m³
Step 3 — Cement and sand
CM 1:6 has 1 + 6 = 7 parts.
- Cement = 1.524 ÷ 7 = 0.2177 m³ × 1,440 kg/m³ = 314 kg = 6.27 bags of 50 kg
- Sand = 1.524 × 6 ÷ 7 = 1.306 m³
Cement and sand per 100 m² of plaster
| Plaster | Typical use | Wet volume | Dry volume | Cement | Sand |
|---|---|---|---|---|---|
| 6 mm, CM 1:3 | Ceiling plaster | 0.60 m³ | 0.762 m³ | 5.49 bags (274 kg) | 0.572 m³ |
| 12 mm, CM 1:6 | Inside walls (brick face) | 1.20 m³ | 1.524 m³ | 6.27 bags (314 kg) | 1.306 m³ |
| 12 mm, CM 1:4 | Inside walls, richer mix | 1.20 m³ | 1.524 m³ | 8.78 bags (439 kg) | 1.219 m³ |
| 15 mm, CM 1:6 | Rough side of a brick wall | 1.50 m³ | 1.905 m³ | 7.84 bags (392 kg) | 1.633 m³ |
| 20 mm, CM 1:4 | External plaster (in two coats) | 2.00 m³ | 2.540 m³ | 14.63 bags (732 kg) | 2.032 m³ |
Why your rate analysis may show more cement
The method above is the textbook quantity of mortar on a true surface. Departmental analyses of rates allow more — for uneven brickwork, filling joints, wastage and the extra cement a richer first coat takes — so a schedule-of-rates build-up for 12 mm CM 1:6 usually carries more cement per square metre than this figure. Use the textbook figure to check, and your contract's analysis to bill.
CivilOS's calculator gives the same figures for any area, thickness and mix with every step shown, and the BOQ prices the plaster item on CPWD DSR 2023 or your State schedule.
Estimate plaster in CivilOS →Frequently asked questions
How many cement bags are needed for 100 m² of 12 mm plaster?
About 6.3 bags of 50 kg in CM 1:6, by the dry-volume method (wet volume 1.2 m³ × 1.27, one part in seven). Add 5–10 % for uneven surfaces and wastage.
What is the dry volume factor for plaster?
1.27 is the usual factor for plaster mortar; some offices use 1.33 to include more for wastage. Use the one your organisation's estimates use, consistently.
Which mix is used for plaster?
Commonly CM 1:6 for inside walls on brick, CM 1:4 for a richer inside or external finish, and CM 1:3 for thin ceiling plaster. The specification of the work governs.
How is plaster measured for a bill?
In square metres of finished surface, with openings deducted or not as IS 1200 Part 12 lays down: small openings are ignored, larger ones are deducted with jambs and soffits added.