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Free painter & decorator calculator
Paint calculator: how much paint you need for a room
Enter the walls, the doors and windows, the ceiling and the woodwork, and see how many litres and tins to buy. Coverage comes from the makers' datasheets: Dulux Trade vinyl matt up to 17m² per litre, retail matt about 13, contract matt 15, budget 10, gloss 18, smooth masonry 15 and pebbledash 5, with 10% added so you do not run out on the last wall.
What you need
Walls
- Wall area
- 30.6 m²after 3.0m² of doors, windows and other openings
- Retail matt or silk
- 5.2 litres2 coats at 13m² per litre, plus 10%Retail matt 12–13m²/L
- Emulsion tins
- 1 × 5L, 1 × 2.5L trade buys 10L
Woodwork
- Woodwork area
- 7.0 m²1 door at 4m² (both faces, lining and architrave), 1 window at 1m², 13.0m of skirting at 0.15m² a metre
- Satinwood or eggshell
- 1 litres2 coats at 16m² per litre, plus 10%Satinwood/eggshell ~16m²/L
- Undercoat
- 0.4 litres1 coat at 17m² per litre, 6 hours before the top coat. Bare wood needs a primer firstDulux Trade Undercoat
- Woodwork tins
- 1 × 1L top coat, 1 × 1L undercoat
Prep and sundries
- Sugar soap
- 1 litres of concentrate1 litre cleans about 40m²
- Filler
- 1 tubs
- Decorators' caulk
- 3 × 310ml tubesceiling line, skirting and frames, about 12m a tube
- Sandpaper
- 4 sheets
- Masking tape
- 1 × 50m rollsceiling line, skirting line, 5m a door and 4m a window
- Dust sheets
- 2 sheets
- Roller sleeves
- 1 sleevesone per 100m² painted
Round up to whole packs and bags. Figures include the wastage you chose and match TradeCalc in the app.
For painter & decorators: turn this into a quote
In the app, TradeCalc hands these quantities straight to ProQuote with your regional material prices, and the customer gets a branded PDF. Free to download.
Or claim your free profile link nowHow the maths works
- Wall area is the total wall length times the height, less 1.6m² for each door, 1.4m² for each window (B&Q's allowances) and anything else you will not paint.
- That net area is multiplied by the coats and divided by the coverage for the grade: trade vinyl or durable matt 16m² per litre (Dulux Trade Vinyl Matt says up to 17, Crown Clean Extreme 14), retail matt 13, contract matt 15 (Dulux Supermatt up to 18 before thinning), budget 10 (what the B&Q and Wickes calculators assume). Then 10% is added.
- New or bare plaster gets a mist coat of the same emulsion thinned up to 1 part water to 5 parts paint (Dulux Trade), which uses about 80% of a full coat. It is not a separate primer, and painted walls in good condition do not need it.
- The ceiling is worked out on its own at the same grade because it is usually a different tin: ceiling white or contract matt.
- Woodwork is worked from the joinery, not the walls: 4m² per door for both faces, lining and architrave, 1m² per window, and 0.15m² per metre of skirting. Two coats of gloss at 18m² per litre (Dulux Trade High Gloss) or satinwood at 16, over one coat of undercoat at 17 (Dulux Trade Undercoat).
- Masonry paint covers 15m² per litre on smooth render (Dulux Weathershield Smooth, up to 16) and only 5 on pebbledash or rough render. Thin the first coat on bare masonry 1 part water to 5.
- Tins are 10L, 5L and 2.5L for emulsion and 5L, 2.5L and 1L for woodwork paint. Prep sundries: a litre of sugar soap per 40m², a tub of filler per 50m², masking tape for the ceiling and skirting lines plus 5m a door and 4m a window, a dust sheet per 20m² and a roller sleeve per 100m² painted.
Worked example
A 4m by 3m room with 2.4m walls has 33.6m² of wall. Take off 1.6m² for the door and 1.4m² for the window and it is 30.6m². Two coats of retail matt at 13m² per litre with 10% extra is 5.2 litres, so one 5L tin and one 2.5L tin. The door, window and 13m of skirting are 7m² of woodwork: 1 litre of satinwood for two coats and 0.4 litres of undercoat.
Questions people ask
How much paint do I need for a room?
Add up the wall lengths, multiply by the height, take off 1.6m² a door and 1.4m² a window, then multiply by the coats and divide by the coverage on the tin. For a 4m by 3m bedroom that is about 5 litres of retail matt for two coats on the walls, or about 4 litres of a trade matt.
How many square metres does a litre of paint cover?
Dulux Trade Vinyl Matt says up to 17m² per litre and Supermatt up to 18, Crown Trade Clean Extreme up to 14, retail matt about 12 to 13, and the merchants' calculators assume a flat 10. Gloss is about 18, undercoat 17. Smooth masonry paint does 15 to 16 and pebbledash only 4 to 6. Rough or porous surfaces always use more.
Do I need to prime new plaster?
Not with a primer. Bare plaster gets a mist coat: the same emulsion thinned with water, up to 1 part water to 5 parts paint for Dulux Trade Vinyl Matt, 1:3 for Supermatt, about 40% for Crown. Full-strength paint on bare plaster dries too fast and peels. Bare wood and metal do need a proper primer before undercoat and gloss.
Do I need two coats?
Nearly always. Dulux recommends two full coats; one may do if the new colour is close to the old one, and a strong colour change or a mist-coated wall can need three. Dark to light takes more than light to dark.
What paint for skirting and doors?
Woodwork gets an undercoat then gloss, satinwood or eggshell, not emulsion. Gloss is the toughest and shiniest, satinwood the usual modern choice, eggshell the flattest. Water-based versions stay white longer; oil-based flow out better but yellow over time.
Is it cheaper to buy a 10 litre tin?
Usually, per litre, which is why trade buys 10L (Dulux Supermatt comes in 5, 10 and 12L; Crown in 10L). Only buy the bigger tin if the numbers here say you need it: leftover paint keeps for touch-ups but a full spare tin is money on a shelf.
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