Short answer
How much cement and sand do I need for plaster? For 100 sq ft of plaster 12 mm thick, plan about 0.98 bags of cement and 4.8 cft of sand in a 1:4 mix, or about 0.70 bags and 5.1 cft in a 1:6 mix. These include a 20 percent allowance for uneven walls and waste. Your engineer chooses the mix and thickness.
On this page (13)
- How much cement and sand for 100 sq ft of plaster?
- What does the table show for each mix?
- How is the quantity worked out?
- Which doors and windows do I take off?
- Worked example: a 10 ft × 12 ft room
- How thick should plaster be?
- Which mix should I use: 1:3, 1:4, 1:5 or 1:6?
- How good sand and good practice affect the result
- What does the calculator leave out?
- Frequently asked questions
- Related guides
- Work out your quantities
- Sources
Need quantities? Plaster quantity calculator
You know the plaster area of your house. Now you need to know how many bags of cement and how much sand to order. This page gives you the numbers in simple steps. It also shows how the numbers are worked out, so you can check any quote from your contractor.
How much cement and sand for 100 sq ft of plaster?
For plaster 12 mm thick, with a 20 percent allowance:
- 1:4 mix: about 0.98 bags of 50 kg cement and 4.8 cft of sand.
- 1:6 mix: about 0.70 bags of cement and 5.1 cft of sand.
So a rough rule is one bag of cement per 100 sq ft for a 1:4 mix, and about 0.7 bag for a 1:6 mix, at 12 mm. A richer mix uses more cement. Use the plaster quantity calculator for your own wall.
What does the table show for each mix?
The table shows the cement and sand for 100 sq ft, with the 20 percent allowance already added.
| Mix | 12 mm: cement (bags) | 12 mm: sand (cft) | 15 mm: cement (bags) | 15 mm: sand (cft) |
|---|---|---|---|---|
| 1:3 | 1.22 | 4.5 | 1.53 | 5.6 |
| 1:4 | 0.98 | 4.8 | 1.22 | 6.0 |
| 1:5 | 0.82 | 5.0 | 1.02 | 6.3 |
| 1:6 | 0.70 | 5.1 | 0.87 | 6.4 |
Sand is loose, dry sand. Cement is in 50 kg bags.
How is the quantity worked out?
Follow these steps for any wall.
- Find the area. Length times height, in square feet. Take off big doors and windows (see below).
- Find the wet volume. Area times thickness. For 100 sq ft at 12 mm, that is 9.29 square metres times 0.012 metre, which is 0.111 cubic metres.
- Find the dry volume. Wet mortar needs more dry cement and sand than its own volume, because the mix shrinks when water is added. This site uses a factor of 1.27, so the dry volume is 0.142 cubic metres.
- Split by the mix. In a 1:4 mix, 1 part in 5 is cement and 4 parts in 5 are sand. In a 1:6 mix, 1 part in 7 is cement.
- Change cement to bags. Cement weighs about 1,440 kg per cubic metre (IS 1661), so a 50 kg bag is about 0.0347 cubic metres.
- Add the allowance. Plaster loses more mortar than brickwork because of uneven walls and waste. This page uses 20 percent. Then round the cement up to whole bags at the end.
Which doors and windows do I take off?
IS 1200 (Part 12) is the standard for measuring plaster. It says small openings of 0.5 square metre (about 5.4 sq ft) or less are not taken off. The calculator takes off larger openings in full, and does not add back their sides. This can make your number a little low if you have large openings, so ask your contractor how they measure.
Worked example: a 10 ft × 12 ft room
These sizes are an example. The room is 10 ft by 12 ft inside and 10 ft high. It has one door of 7 × 3 ft and two windows of 4 × 4 ft. The walls get 12 mm of 1:6 plaster and the ceiling gets 10 mm of 1:4. Allowance is 20 percent.
- Walls: 44 ft × 10 ft is 440 sq ft. The openings are 21 + 16 + 16 = 53 sq ft, so the plaster area is 387 sq ft. That needs 2.71 bags of cement and 19.9 cft of sand.
- Ceiling: 12 ft × 10 ft is 120 sq ft. That needs 0.98 bag of cement and 4.8 cft of sand.
- Total: 3.68 bags, so buy 4 bags. Sand is 24.7 cft, about 0.70 cubic metres.
If you do not take off the openings at all, the wall plaster rises to 440 sq ft and the total goes to 4.05 bags, so you would buy 5 bags. Check your opening sizes carefully, because they can change the order by a whole bag.
How thick should plaster be?
IS 1661 gives these ranges. Your engineer decides the exact thickness for your wall.
- One coat: 10 to 15 mm.
- Two coats: a base coat of 10 to 12 mm and a finishing coat of 3 to 8 mm. The total is about 20 mm and not normally more.
- Three coats: a base coat of 10 to 15 mm, a second coat of 3 to 8 mm and a thin finishing coat of 3 to 5 mm. The total is about 25 mm and not normally more.
- Ceilings: on concrete ceilings poured in place, the total plaster should not be more than 15 mm.
Thick plaster applied in one go is more likely to crack. The calculator accepts 6 to 25 mm and shows a note when you go above 15 mm.
Which mix should I use: 1:3, 1:4, 1:5 or 1:6?
The standard lists cement and sand mixes of 1:3, 1:4 and 1:6. It does not say which one goes on which wall, inside or outside, or on a ceiling. Many builders use a leaner mix such as 1:6 inside and a richer mix such as 1:4 outside, but that is common practice and not a rule. 1:5 is not in the table but is also used. A richer mix uses more cement and shrinks more as it dries, so it can crack more. Your engineer chooses the mix for each surface.
How good sand and good practice affect the result
- Sand. IS 1542 asks for sand with not more than 5 percent of clay, silt and dust. Dirty sand makes weak plaster that cracks and peels. Damp sand takes up more space than dry sand, so order a little extra when sand is wet. See Sand bulking.
- Mixing. Mix only as much mortar as you can use in about half an hour.
- Curing. Plaster needs to stay damp while it hardens. IS 1661 asks for each base coat to be kept damp until the next coat goes on, up to 7 days, and the finishing coat for at least 7 days. Ask your engineer for the days your wall needs.
- Walls made of AAC blocks. They need a plaster mix and method suited to them. Follow the block maker and your engineer. See Red brick vs fly ash brick vs AAC block.
What does the calculator leave out?
- Lime or gypsum plaster, bonding agents, mesh and special finishes.
- Cement for the first rough coat on very uneven or smooth concrete.
- Damp-sand allowance, labour and cost. Prices change, so this page gives none.
Frequently asked questions
How many bags of cement for 100 sq ft of plaster?
About 0.98 bags for a 1:4 mix and 0.70 bags for a 1:6 mix, at 12 mm with a 20 percent allowance.
How much sand for 100 sq ft of plaster?
About 4.8 cft for 1:4 and 5.1 cft for 1:6, at 12 mm with a 20 percent allowance.
How many sq ft does one bag of cement plaster?
About 102 sq ft at 12 mm in a 1:4 mix, and about 143 sq ft in a 1:6 mix, with a 20 percent allowance.
Why is the allowance 20 percent and not 5 percent?
Plaster loses more mortar than brickwork, because walls are uneven and some mortar falls and dries unused. At 5 percent you will usually run short. The 20 percent is a common starting point on this site, not an Indian Standard figure.
Do I take off doors and windows?
Take off openings larger than 0.5 square metre (about 5.4 sq ft). The calculator does it for you.
Can I plaster thicker than 20 mm in one go?
No. Thick plaster needs more coats, and your engineer should decide how.
Related guides
- Hairline cracks in plaster: causes and what to do
- Mortar ratio for brick walls: 1:4, 1:5 or 1:6?
- How many bricks for 100 sq ft of wall? Assumptions shown
This guide is general information. Read the disclaimer. The mix, thickness and number of coats for your walls are set by your engineer.
Work out your quantities
- Plaster quantity calculator: Estimate the cement bags and sand for cement plaster on a wall or ceiling, from its size, thickness and mix, with doors and windows taken off.
Sources
- IS 1661:1972, Code of Practice for Application of Cement and Cement-Lime Plaster Finishes
- IS 1200 (Part 12):1976, Method of Measurement of Building and Civil Engineering Works: Plastering and Pointing
- IS 1542:1992, Sand for Plaster
General information only. It is not a structural design or professional advice. Ask a licensed structural engineer or architect to check your plans and site.