Plaster Quantity Calculation: Cement, Sand, Water and Labour per Sqm

One square metre of 12 mm cement plaster in a 1:6 mix takes about 3.1 kg of cement and 0.013 m³ of sand. That is the whole of a plaster quantity calculation in one line: an area off the drawing, a thickness, a mix ratio and a factor that turns wet plaster back into the dry cement and sand you have to buy.

The method comes from three Indian Standards. IS 1200 (Part 12) says how a plastered area is measured. IS 1661 sets the thickness and mix for each coat. IS 7272 gives the labour days per square metre. This guide works through all of it with one wall, and gives a table for 12 mm, 15 mm and 20 mm plaster in 1:3, 1:4 and 1:6.

It carries no rupee figures. Plaster rates and labour rates change from town to town and year to year. The quantities below do not.

What is the formula for plaster quantity?

Five steps, always in this order:

1. Area: measure the surface to be plastered in square metres, with the deductions IS 1200 allows for doors and windows.
2. Wet volume: area × thickness in metres. A 12 mm coat is 0.012 m.
3. Dry volume: wet volume × 1.27. This is the loose cement and sand that shrinks down into that wet layer.
4. Cement: dry volume ÷ (sum of the mix parts). For 1:6 the sum is 7. Multiply the result by 1,440 to get kilograms, and divide by 50 for bags.
5. Sand: cement volume × the sand part. For 1:6, six times the cement volume.

Written as one formula for a cement-sand mix of 1:n:

Cement (kg) = Area × thickness × 1.27 ÷ (1 + n) × 1,440

The 1,440 is not a guess. IS 1661 clause 11.1.2 says that for proportioning, one cubic metre of cement is taken to weigh about 1,440 kg. A 50 kg bag therefore fills about 0.0347 m³, the same figure the building material calculation guide uses for concrete.

How do you measure the plaster area?

Measure the wall between the walls or partitions on each side for length. Measure height from the top of the floor, or the top of the skirting, up to the ceiling. Those are the rules in IS 1200 (Part 12) clause 3.12, and they mean a tiled skirting is not plastered behind and is not counted. Ceilings are measured between the walls (clause 3.9).

Openings are where people go wrong. You do not just subtract every door and window. Clause 3.8 sets three bands by the size of each opening:

The logic is simple once you see it. The plaster that goes round the inside of a small opening, on its jambs and sill, roughly makes up for the hole. So a ventilator costs you no plaster at all, and a normal door or window is taken off only once for a wall plastered on both faces. A big opening such as a shop shutter loses its full area from both faces, and its sides are then measured as separate strips.

Two more rules from the same part matter on a house. A band of plaster 30 cm wide or less, such as a sill band or a column face, is measured in running metres, not square metres (clause 3.4). And dubbing, the extra plaster used to fill a hollow or bring a crooked wall true, is described separately (clause 3.1.3), so it does not hide inside your square metres. How these units sit in a full bill of quantities is covered in the construction estimate format guide.

Why multiply by 1.27 for plaster?

Loose cement and sand have air between the grains. When water goes in and the mason presses the mortar onto the wall, that air comes out and the heap shrinks. So 1 m³ of finished plaster on the wall needs more than 1 m³ of dry material in the mixing tray.

Indian estimators use about 1.27 for plaster and mortar. Concrete uses 1.54, because it also has coarse aggregate with large voids. Some sites round the plaster factor up to 1.33 or 1.35 so that a little wastage rides inside the same number. Either works, but use one. Do not take 1.35 and then add a wastage percentage on top, or you will count the spill twice.

For the wall worked below, 1.27 gives 3.6 bags of cement and 1.35 gives 3.9. On one wall that is a few kilograms. On a whole house it is a few bags, which is why it is worth agreeing the factor with your contractor before the quantities are signed.

How much cement and sand for plaster per sqm?

The table is worked at 1.27, 1,440 kg per m³ of cement and a 50 kg bag. Read the per-square-metre column for small jobs and the per-100 m² columns when you are ordering for a floor. 100 m² is about 1,076 sq ft.

Notice what the mix does. Going from 1:6 to 1:4 at the same thickness adds about 40% more cement and takes away a little sand. Going from 12 mm to 15 mm adds 25% of everything. Thickness is the number to watch on site, because a mason who lays 16 mm where the drawing says 12 mm uses a third more material and nobody sees it once the wall is painted.

To turn bags into money, check the current cement price per bag in your area on the day you order. What a bag is allowed to weigh, and its volume, is set out in cement bag weight and size.

Which thickness and mix: 12 mm, 15 mm or 20 mm, 1:4 or 1:6?

IS 1661 Table 2 lists the mixes and coat thicknesses it recommends. A single coat, for inside or outside walls, is 10 to 15 mm in cement-sand 1:3, 1:4 or 1:6, or a cement-lime-sand mix such as 1:1:6. Two-coat work has a 10 to 12 mm backing coat and a 3 to 8 mm finishing coat. Clause 7.3.2 says the total for two coats should not normally go past 20 mm, and should not go past 15 mm on the underside of a cast-in-place concrete slab. Three-coat work, used on very rough stone, stops at about 25 mm.

The standard does not tie a particular mix to a particular wall. That choice sits in your drawing or contract. On Indian house sites the usual pattern is a richer 1:4 on outside walls, which take rain and sun, and a leaner 1:6 inside. A 12 mm coat is normal on the smooth face of a brick wall. The rough face of the same wall often needs 15 mm to come out flat.

Block walls change the sum. Factory-cut AAC blocks give a truer face than handmade bricks, so the wall needs less plaster to come flat, as the AAC blocks vs red bricks comparison explains. The cement type matters too. PPC or 43 grade cement suits plaster better than a fast-setting 53 grade, for the reasons set out in choosing cement for a house.

Worked example: a 10 m wall plastered on both faces

Take an inside wall 10 m long and 3 m high, plastered on both faces in 12 mm cement plaster 1:6. It has one door, 1.0 m × 2.1 m, with a frame narrower than the wall. It has one ventilator, 0.6 m × 0.6 m.

Now the five steps:

Order 4 bags, not 3.6. Cement comes in whole bags and a part bag left open on site goes hard. If the same wall had a 2.4 m × 2.1 m rolling shutter instead of a door, at 5.04 m² it would come off both faces, and its two sides and top would be measured as narrow strips.

How much water does plaster need?

IS 1661 gives one figure. For general cement plaster in 1:3, the mixing water is about 70% of the weight of cement (clause 11.1.4). For 12 mm plaster in 1:3 that works out to about 3.8 litres per square metre.

The same clause says the figure moves with the sand’s moisture, the weather, the richness of the mix, any lime and any admixture. Leaner mixes such as 1:6 are brought to a workable consistency on site, following IS 2250, the code for masonry mortars. So do not pour water by a fixed ratio. Add it until the mortar holds on the trowel and spreads without slumping. A plasticiser can bring the same workability with less water, as covered in the guide to admixtures.

Curing needs far more water than mixing. Clause 16.1 says each coat is kept damp continuously until the next coat goes on, or for up to 7 days. On a hot wall in May that can mean wetting it several times a day. The standard gives the reason in the same clause: curing is what develops the strength and density of the plaster.

How many labour days does plastering take?

IS 7272 (Part 1) gives labour output constants for building work in the north zone, which it defines as Punjab, Haryana, Delhi, Uttar Pradesh and Rajasthan. Each figure is days of an 8-hour working day per square metre, with mixing of the mortar included.

Put another way, 0.08 days per square metre is about 12.5 m² per mason per day on an inside wall. The standard has no separate line for 12 mm, so use the 15 mm figure as your planning number. For the 57.9 m² wall above, that comes to about 4.6 mason-days and 5.8 helper-days. Most sites today give the water carrier’s work to a helper with a hose, so the last two columns often become one person.

These are planning figures from a 1974 standard, written for one region. Scaffolding height, the state of the wall and how many coats the job needs all move the real output. Use them to check that a contractor’s labour count is in the right range, not as a target for the gang.

What sand should be used for plaster?

Plaster sand has its own standard, IS 1542. Its Table 1 asks that all of it pass a 10 mm sieve, 95 to 100% pass 4.75 mm and no more than 15% pass the finest 150 micron sieve. That grading gives a fineness modulus, a number for how coarse the sand is, of about 1.2 to 2.2. The standard prefers at least 1.5 for river sand and 1.4 for crushed sand.

IS 1661 adds a detail masons know by feel. For single-coat work it asks for a fineness modulus near 1.5. Where two or three coats are used, the under coats should take coarser sand, with a fineness modulus of at least 2.0. Very fine sand weakens the plaster, so it is improved by mixing in some coarse sand. Where river sand is short, crushed plaster sand is now common, and the quarry dust and M-sand guide covers how it is graded and washed.

Sand bought by the cubic foot also bulks when damp, so a truck of wet sand holds less sand than its volume says. That is one more reason to agree your dry volume factor before measuring the load.

Where plaster fits in a house budget

Plaster is one line in the finishing stage, after the brickwork and before tiling and paint. The tiles that follow are counted, with their cutting waste, in how to calculate tile quantity. The quantities on this page feed the estimate the same way the steel does in a bar bending schedule. The house construction cost calculator puts the plaster total next to every other block of the budget. Outside walls in heavy rain areas often get a waterproofing additive in the outer coat, and the waterproofing chemicals guide explains which type goes where.

Plaster comes last because the frame comes first: the slabs, beams and columns it covers are cast before a mason picks up a trowel. If you are planning that concrete work, compare live concrete mixer models and connect with a dealer. More estimating guides sit under construction cost.

Prices, specifications and features are indicative, vary by variant, location and date, and should always be confirmed with the official OEM or authorised dealer before any purchase decision. DesiMachines is not liable for decisions taken on the basis of information that may have changed after publication.

Code references: IS 1661 : 1972 (application of cement and cement-lime plaster finishes), Table 2 and clauses 7.3.2, 11.1.2, 11.1.4 and 16.1; IS 1200 (Part 12) : 1976 (method of measurement, plastering and pointing), clauses 3.1.3, 3.4, 3.8, 3.9 and 3.12; IS 7272 (Part 1) : 1974 (labour output constants, north zone), Table 1 item vii, with Amendment No. 1 (8-hour day); IS 1542 : 1992 (sand for plaster), Table 1 and clause 5.2. Quantities use a dry volume factor of 1.27 and 1,440 kg per m³ of cement. The worked example is an illustration; your drawing and contract specification decide the mix and thickness.