Plaster Calculator: Cement, Sand and Cost
100 sq ft of 12 mm cement plaster in 1:6 needs about 0.7 bag of cement and 0.146 m³ (5.2 cft) of sand, including 15% for unevenness and wastage. Enter your surface area or walls below for cement bags, sand and a cost range.
Calculate plaster cement, sand and cost
Count each plastered face separately. This tool deducts the openings you enter in full; use the contract’s IS 1200 rules when preparing a bill.
Same formula as the cement calculator: wet volume × 1.33 = dry volume; cement density 1,440 kg/m³ and bag size 50 kg. The 15% allowance is editable, not an IS code requirement. Location does not multiply quantities again.
- Net plastered surface
- 10 m² / 107.64 sq ft
- Wet mortar before allowance
- 0.12 m³
- Wet mortar including allowance
- 0.138 m³
- Dry mortar volume
- 0.18354 m³
- Cement (50 kg bags)
- 0.7551 (1 whole bag)
- Sand
- 0.15732 m³ / 5.556 cft
- Budget range
- ₹3,229–₹3,444
Budget = net area × ₹30–32/sq ft from the rate guide. It does not reprice cement, sand or the allowance. Repairs, mesh, unusual access, putty and paint are separate.
Why the CPWD table in the rate guide differs
For this area, the guide’s DAR basis gives 0.144 m³ scheduled mortar, 0.72 cement bags and 0.15408 m³ sand. It already includes schedule allowances. The primary result above uses the cement calculator’s 1.33 dry factor and your 15% allowance. These are alternative estimating bases; do not combine them.
Read the plaster rate analysis and source coefficientsMeasure perimeter × height less doors and windows with the square feet calculator before estimating plaster.
For the finish over plaster, the wall putty calculator uses published coverage to estimate kg and bags.
Worked example: 10 m², 12 mm internal plaster, 1:6
10 m² of 12 mm plaster in 1:6 needs 0.76 bag of cement and 0.157 m³ of sand, with a 15% allowance. The area is one 4 m × 3 m wall face less 2 m² of openings.
- Nominal wet volume = 10 × 12 ÷ 1,000 = 0.12 m³.
- With 15% allowance: 0.12 × 1.15 = 0.138 m³.
- Dry volume = 0.138 × 1.33 = 0.18354 m³.
- Cement = 0.18354 ÷ 7 = 0.02622 m³; × 1,440 = 37.7568 kg; ÷ 50 = 0.755136 bags. Buy 1 whole bag for this isolated job; combine project quantities before rounding.
- Sand = 0.18354 × 6 ÷ 7 = 0.15732 m³; × 35.3147 = 5.555708604 cft.
- At the guide’s ₹30–32/sq ft reference, area = 10 × 10.7639 = 107.639 sq ft. Budget = ₹3,229–₹3,444, an all-in reference rather than a priced material list.
The same settings in the cement calculator’s plaster mode return the same result. Internal/external is a specification preset; it does not multiply quantities again. To buy sand by the brass or tonne, the sand calculator converts the same figure.
Cement and sand per 100 sq ft
100 sq ft of 12 mm 1:6 plaster takes about 0.70 bag of cement by our formula, or 0.67 bag on CPWD DAR constants. The formula columns include a 15% allowance. The last column uses the schedule basis in the plaster rate per sq ft guide, with its allowance already included.
| Specification | Formula: bags | Formula: sand m³ (cft) | DAR: bags / sand m³ |
|---|---|---|---|
| 12 mm, 1:6 | 0.702 | 0.146 (5.16) | 0.669 / 0.143 |
| 12 mm, 1:4 | 0.982 | 0.136 (4.82) | 1.017 / 0.143 |
| 15 mm, 1:6 | 0.877 | 0.183 (6.45) | 0.799 / 0.171 |
| 20 mm, 1:6 | 1.169 | 0.244 (8.6) | 1.041 / 0.223 |
| 20 mm, 1:4 | 1.637 | 0.227 (8.03) | 1.582 / 0.223 |
For 10 m² at 12 mm 1:6, DAR uses 0.144 m³ mortar × 5 bags/m³ = 0.72 bags, and 0.144 × 1.07 = 0.15408 m³ sand. The formula uses 0.138 m³ wet mortar and 0.755 bags. No single allowance makes the two methods match for both cement and sand.
Assumptions, rates and sources
Each input below is editable or sourced, reviewed 20 October 2026. Results are quantities to buy; billing follows the contract’s measurement rules.
| Input or rule | Basis and source |
|---|---|
| Dry factor 1.33; 15% editable allowance | Shared cement calculator assumptions, reviewed October 2026. The dry factor converts wet to dry mortar; the allowance covers unevenness and loss. Neither is claimed as a mandatory IS factor. |
| 50 kg cement bags; 1,440 kg/m³ loose density | Same shared material engine. Loose volume conversion is an estimating assumption, not hardened cement density. |
| DAR reference: 0.144/0.172/0.224 m³ per 10 m² | 12/15/20 mm schedule mortar from the rate guide’s CPWD DAR 2023 analysis and source list. CM 1:6 uses 5 bags/m³; CM 1:4 uses 7.6; sand 1.07 m³ per m³ mortar. No extra wastage or dry factor is applied. |
| Internal ₹30–32; external ₹43–45 per sq ft | Rounded reference scenarios from the October 2026 plaster rate guide for 12 mm 1:6 and 20 mm 1:4. Source scopes differ; confirm quote inclusions. Other specifications require entered local rates. |
| Openings and plastered faces | Physical area is deducted in full here. For contractual measurement see IS 1200 (Part 12):1976 and the guide’s opening examples. |
Common mistakes
The usual errors are using floor area instead of wall area and adding wastage twice.
- Entering floor area instead of the wall and ceiling surfaces receiving plaster.
- Counting both faces as one, or deducting the same opening twice from a single face.
- Using the concrete dry factor 1.54 for mortar. This tool reuses the existing mortar factor 1.33.
- Adding 15% again to a schedule quantity that already contains its allowance.
- Applying a 12 mm reference rate to 20 mm work. Match thickness, mix, substrate and access before comparing quotes.
- Including putty and paint inside a cement plaster rate without checking the scope.
Wall putty cost per sq ft is a separate item
Putty is a finish over a prepared surface, not a substitute for this cement-and-sand calculation. Measure its treated area and price the specified product, coat thickness and preparation separately. The plaster and putty rate guide compares schedule items with reported rates; use its stated scope before choosing a rate.
For the substrate, use the AAC block calculator or brick calculator. See all construction calculators.
Frequently asked questions
How do I calculate plaster cement and sand?
Wet mortar = net plastered area × thickness in metres × (1 + allowance/100). Dry volume = wet mortar × 1.33. For a 1:n mix, cement bags = dry volume ÷ (1 + n) × 1,440 ÷ 50, and sand = dry volume × n ÷ (1 + n).
How much cement is needed for 100 sq ft of plaster?
About 0.70 bag of cement and 0.146 m³ (5.2 cft) of sand for 12 mm plaster in 1:6, including 15% for unevenness and wastage. CPWD DAR constants, used in our plaster rate guide, give about 0.67 bag and 0.143 m³. Use one basis; don’t mix their allowances.
Does this agree with the cement calculator?
Yes. Both use the same formula, area conversion, thickness, ratio and allowance. For 10 m² of 12 mm 1:6 plaster with 15%, both return 0.138 m³ wet mortar, 0.184 m³ dry mortar, 0.755 cement bag and 0.157 m³ sand.
Why does the plaster rate guide show different material quantities?
The guide uses CPWD DAR mortar quantities and per-m³ cement and sand constants. This calculator uses plaster volume, a 1.33 dry factor and your allowance. The expandable DAR note under the result shows the guide’s figures for your area, with no extra wastage added.
What thickness and mix should I use?
Use the project specification. Common starting points are 12 mm in 1:6 for internal walls and 20 mm in 1:4 for external walls, which the Internal and External presets load. The tool also offers 6 and 15 mm, and 1:3 or 1:5.
Are doors and windows deducted?
Yes, in full, because the tool estimates material to buy. For billing, IS 1200 Part 12 deducts openings by size and adds reveals by rule, so a bill can differ from this figure.
What is the plastering cost range?
About ₹30–32 per sq ft for 12 mm internal plaster in 1:6 and ₹43–45 for 20 mm external plaster in 1:4, with material and labour, from our October 2026 plaster rate guide. For other specifications, enter your local all-in rate; budget = area × rate.
Does plaster cost include wall putty?
No. Cement plaster, wall putty, primer and paint are separate items. Putty cost depends on coats, preparation, product coverage and labour; the plaster rate guide compares putty schedule rates with reported market rates. Use the paint calculator for putty kg.
Plastering a whole building? Get a BOQ from your drawings with internal and external plaster measured face by face.