Paint Quantity Calculation: Area, Coverage per Litre, Putty and Primer

One litre of interior emulsion covers about 130 to 150 sq ft of new wall in two coats. A 12 ft × 10 ft bedroom with a 10 ft ceiling has about 411 sq ft of wall to paint once the door and window come off, so its walls take roughly 3 litres.

That is a paint quantity calculation: the painted area, the number of coats, and the coverage the maker prints for the product. Each of the three has a trap. The wall area follows rules for doors and windows set in IS 1200 (Part 13). Doors, windows and grilles are measured with multiplying factors from IS 1200 (Part 15). And coverage can differ by two times between two tins, for a reason this guide explains.

There are no rupee figures here. Paint prices change with brand, shade and year. The litres a wall needs do not.

What is the formula for paint quantity?

Paint needed is the painted area divided by the coverage per litre for the number of coats you plan. Five steps, in this order:

1. Measure each wall and the ceiling: length × height.
2. Take off doors and windows the way IS 1200 allows. Small openings are not taken off at all.
3. Measure doors, windows and grilles separately with the factors further down. They usually get enamel, a different paint.
4. Pick the coverage for that product and that number of coats.
5. Divide, then round up to whole tins.

Paint (litres) = painted area (sq ft) ÷ two-coat coverage (sq ft per litre)

Most Indian paint sheets print coverage in sq ft per litre, while IS 1200 measures in square metres. One square metre is 10.76 sq ft. Convert once and stay in one unit.

Use the maker’s two-coat figure when the sheet gives one. When it gives only a one-coat figure, half of it is a fair planning number. On the sheets that print both, the two-coat figure comes out at about half: 250 to 270 sq ft against 130 to 150 for an interior emulsion, 185 to 225 against 95 to 110 for a gloss enamel.

How do you measure the wall area for painting?

IS 1200 (Part 13) is the Indian Standard for measuring whitewash, distemper and paint on building surfaces. It measures all work net, in square metres (clause 3.1). Walls, ceilings and sloping roofs are measured separately (clause 2.8), which helps, because the ceiling often takes a different paint.

The rule people get wrong is the one for openings. Clause 3.2 does not subtract every door and window. It works by the size of each opening:

The reveal is the strip of wall between the frame and the face of the wall. The thinking behind the bands is simple. Paint that goes round the sides of a small opening roughly makes up for the hole, so a ventilator costs nothing and an ordinary door is taken off once for a wall painted on both faces.

Pipes and wiring fixed on the wall are not deducted (clause 3.3). Cornices in the wall colour are measured round their shape and added to the wall (clause 3.5).

The same bands decide plaster, so the areas here match the plaster quantity calculation for the same wall. How a painting item sits in a bill of quantities is set out in the construction estimate format guide.

How many sq ft does 1 litre of paint cover?

Coverage depends on the product, so read it from the sheet of the tin you will buy. These are the figures printed on makers’ own product sheets, read in October 2026:

Outside paint covers far less: an outside wall needs about two and a half times the paint of the same area indoors in economy emulsion. Every one of these sheets also warns that actual coverage moves with surface roughness, porosity and the way the paint is put on. A rough wall, or a spray gun, uses more. The Apex sheet adds that some shades need three coats to hide the wall below.

Why does one tin cover twice as much as another?

Because the coats are not equally thick. Paint is part liquid and part solids. The share that stays on the wall after the water dries off is called the volume solids, and the thickness of the dried coat is the dry film thickness, measured in microns. A micron is a thousandth of a millimetre.

From those two numbers, the theoretical coverage is:

Coverage (m² per litre) = volume solids (%) × 10 ÷ dry film thickness (microns)

The technical sheet for Asian Paints Supreme Acrylic Emulsion shows it working. The paint has 34% volume solids, and the sheet gives 8.50 m² per litre at 40 microns, 6.80 at 50 and 5.66 at 60. Put 34 × 10 ÷ 40 into a calculator and you get 8.5.

So a tin that claims a big coverage figure may simply lay a thinner coat. Nerolac’s sheet for Beauty Smooth Super gives 15 to 20 microns per coat by brush, about half the 40 microns on the Supreme Acrylic sheet, and the coverage per coat is higher for exactly that reason. Compare paints at the same film thickness, or by how many coats the sheet asks for, not by the coverage line alone.

The same sum explains thinning. Each sheet gives a water dilution (10 to 15% by volume for Supreme Acrylic, 15 to 20% for Apcolite Premium Emulsion). Extra water adds no solids. A painter who thins past the sheet spreads each litre further, the coat comes out thinner, and the wall needs one more coat to hide. Theory is also the best case: the sheets list surface profile, uneven application, overspray and losses in the tin and the equipment as reasons real coverage falls short of it.

How do you calculate paint for doors, windows and grilles?

Nobody measures every moulding on a panelled door. IS 1200 (Part 15) measures the door or window flat, including its frame (the chowkat), and multiplies that area by a factor from its Table 1. The factor stands for the extra surface in the panels, edges and bars.

A panelled wooden door 3 ft × 7 ft, frame included, is 21 sq ft. Painted on both sides it counts as 21 × 1.30 × 2 = 54.6 sq ft. At the enamel’s 95 to 110 sq ft per litre for two coats, that is 0.50 to 0.57 litre. A 4 ft × 4 ft window grille counts as 16 sq ft, because the factor of 1 already covers both faces and every bar. A 6 ft × 7 ft collapsible gate counts as 63 sq ft.

The notes under the table settle the usual arguments. The factors include painting the iron fittings in the same shade (Note 3). If a shutter has a gap of more than 15 cm at the top or bottom, that gap comes off first (Note 6). A door that mixes types, such as panels below and glass above, is split at the middle rail and each part takes its own factor (Note 2).

Narrow strips up to 10 cm wide and rainwater pipes go in running metres (clauses 3.3 and 3.7), and structural steel may be measured by weight (clause 3.2). The enamel coverage above was printed for a smooth surface, and bare wood soaks up its first coat, so new joinery is primed first.

Worked example: one bedroom from walls to grille

Take a bedroom 12 ft × 10 ft with a 10 ft ceiling. It has a panelled door 3 ft × 7 ft with the same emulsion on both faces, a window 4 ft × 4 ft with exterior paint on its outer face and its frame set in the middle of the wall, a ventilator 2 ft × 1.5 ft and a window grille 4 ft × 4 ft. The walls get economy interior emulsion in two coats over white cement putty. The door and grille get gloss enamel.

Now the whole room, step by step:

What to buy: one 4 litre tin of wall emulsion, which leaves some for touch-ups, about a litre of ceiling paint, and a 1 litre tin of enamel for the door and grille together. For putty, plan on 40 kg. The sheet’s figure is for rough masonry, so a smooth wall usually leaves some over.

One check is worth doing. The walls and ceiling here add up to 560 sq ft before deductions, which is 4.7 times the 120 sq ft floor. An estimate built on floor area alone runs short in any room with a high ceiling, which is why the walls are measured one by one.

How much putty and primer do you need?

Wall putty is a smooth paste, white cement based or acrylic, spread with a putty knife to fill pores and dents before painting. The sheets class it as an undercoat. The two kinds cover very different areas because they go on at different thicknesses:

Putty is optional on several of these sheets. The Apex exterior system lists it as an optional first step, and the Tractor Emulsion system uses acrylic putty on dents and holes as needed. A true 12 mm plaster coat needs much less putty than a wavy one.

Primer is the first coat that seals the plaster so the finish coat holds and does not soak in. New plaster has to cure before it: the sheets ask for 28 days on new masonry. For the bedroom above, walls and ceiling come to 531 sq ft, and two coats of the anti-damp primer at 200 sq ft per litre per coat need about 5.3 litres. That sheet does not say whether its figure is per litre before or after the 50% water is added. Taking it as before gives the larger quantity, which is the safe side to order on.

The Tractor Emulsion sheet sets out the usual order: sand, prime, putty where needed, sand, a second primer coat, sand, then two finish coats. A wall that shows damp needs the source fixed before any of this, and the waterproofing chemicals guide explains which treatment goes where.

How much paint does the outside of a house need?

More than the inside, for two reasons. Exterior emulsion covers about 55 to 60 sq ft per litre in two coats. And a textured surface has more real area than its flat size, which IS 1200 (Part 13) handles by adding a percentage before you divide:

The plaster finishes are clause 3.6, the sheets clause 3.4, and the jalli figures come from Amendment 1 of 2002, which replaced the old 50% and 70%. Part 15 of the same standard adds 12% for corrugated aluminium sheet.

A front wall 30 ft wide and 20 ft high is 600 sq ft. In smooth plaster it needs 600 ÷ 60 to 600 ÷ 55, about 10 to 11 litres of exterior emulsion. Finish the same wall in sand-faced plaster and it counts as 900 sq ft, which needs 15 to 16.4 litres. The texture choice moves the paint by half again.

A boundary wall is usually painted on both faces, so count both when you work up the compound wall cost. On a two-storey front, painters work from scaffolding or a powered platform, and the scissor lifts guide covers how those platforms reach a wall.

Paint in the finishing order of a house

Paint is the last wet trade. The plaster under it is sized in the plaster quantity guide, the floor finish before it in how to calculate tile quantity, and the other site materials in the building material calculation guide. The house construction cost calculator places the painting total beside every other block of the budget. Paint is also one of the items that can wait for a second phase when money is short, as the low-cost house guide explains. Repainting a finished building is priced through an annual repair estimate, one of the types of estimate made over a building’s life.

All of it sits on a frame of slabs, beams and columns that is cast long before a painter arrives. 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 1200 (Part 13) : 1994 (method of measurement, whitewashing, colour washing, distempering and painting of building surfaces), clauses 2.8, 3.1, 3.2.1, 3.2.2, 3.3, 3.4, 3.5, 3.6 and 3.7 as amended by Amendment No. 1 (2002); IS 1200 (Part 15) : 1987 (method of measurement, painting, polishing, varnishing), clauses 3.2, 3.3, 3.6 and 3.7, Table 1 and its Notes 2, 3 and 6, with Amendment No. 1 (2002). Coverage figures are from the makers’ own product sheets as read in October 2026: Asian Paints Tractor Emulsion (0057), Apex (0012), Apcolite Premium Gloss Enamel, TruCare Exterior Wall Primer (0065), TruCare Red Oxide Metal Primer (0005), Asian Wall Putty (0079), Acrylic Wall Putty (1354), Supreme Acrylic Emulsion and Apcolite Premium Emulsion technical data; Nerolac Beauty Smooth Super, Beauty Ceiling Emulsion and Perma Damp Protect Interior. The worked examples are illustrations; your drawing, the product you buy and its own sheet decide the final quantity.