Paint calculator

How much paint your walls and ceilings need, in litres and tins, with doors and windows taken off.

Sets the tin sizes and the usual door and window sizes.

Rooms

Room 1

Two is usual. Allow a third over a strong colour.

From the tin. Rough or porous walls take more paint.

For new plaster or bare surfaces: one coat before the paint.

Extra for offcuts, spills, breakages and mistakes.

More options

You'll need

Wall paint

6.78 L

Buy 1 × 5 L + 1 × 2.5 L (7.5 L)

Includes 10% for waste.

How it's worked out
  1. Room 1, walls: 2 × (4 m + 3 m) × 2.4 m = 33.6 m²
  2. Room 1, doors and windows: 1 × 1.51 m² + 1 × 1.26 m² = 2.77 m²
  3. Room 1, walls to paint: 33.6 m² − 2.77 m² = 30.83 m²
  4. Walls: 30.83 m² × 2 coats ÷ 10 m²/L = 6.17 L
  5. Walls: 6.17 L + 10% for waste = 6.78 L
  6. Walls: 6.78 L → 1 × 5 L + 1 × 2.5 L = 7.5 L

Estimates only — verify before purchase. Check the quantities against your own measurements and the product's label.

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What it works out

This works out how much paint a room needs: litres for the walls, the ceiling if you're painting it, and a primer or mist coat if the surface is new or bare. It then turns the litres into tins, in the sizes shops sell, so you know what to put in the basket.

It's for emulsion on walls and ceilings. Woodwork, floors and masonry paint spread at different rates, so use the rate on that tin if you're working one of those out.

How it works

Measure each room's length, width and height, or give the wall area if the room isn't a simple box. The calculator works out the area of the walls, then takes off the doors and windows, using a typical door and window for your region (you can change their sizes under More options).

The area to paint is multiplied by the number of coats and divided by the spread rate: how many square metres a litre covers in one coat. The rate on most tins is measured on smooth, sealed walls, so the calculator starts a little lower to allow for real walls. Then the waste allowance goes on top, for the paint left in the tray, the roller and the bottom of the tin.

Finally it picks tins: the combination that leaves the least over, then the one with fewest tins. Sometimes two small tins beat one big one, and the working shows which it chose and why.

A worked example

One room 4 m by 3 m and 2.4 m high, with 1 door and 1 window. Walls only, 2 coats, with a paint that spreads 10 m²/L a coat.

  1. Room 1, walls: 2 × (4 m + 3 m) × 2.4 m = 33.6 m²
  2. Room 1, doors and windows: 1 × 1.51 m² + 1 × 1.26 m² = 2.77 m²
  3. Room 1, walls to paint: 33.6 m² − 2.77 m² = 30.83 m²
  4. Walls: 30.83 m² × 2 coats ÷ 10 m²/L = 6.17 L
  5. Walls: 6.17 L + 10% for waste = 6.78 L
  6. Walls: 6.78 L → 1 × 5 L + 1 × 2.5 L = 7.5 L

The result

  • Wall paint6.78 LBuy 1 × 5 L + 1 × 2.5 L (7.5 L)

These are the calculator's own figures for these measurements, with 10% for waste. Change any of them above and it works it out again.

Common mistakes

  • Forgetting the second coat. One coat rarely hides the colour underneath, even with a one-coat paint. Plan for two, and a third over a strong or dark colour.
  • Trusting the best case on the tin. The figure on the label is for smooth, sealed walls. Textured, porous or patched walls drink more.
  • Skipping the mist coat on new plaster. Fresh plaster soaks up the first coat. A watered-down mist coat seals it so the finish coats go on evenly.
  • Not taking off doors and windows. In a small room they're a good share of the wall area, and you'd buy a tin you don't need.
  • Buying tins from different batches. Colours can vary slightly between batches. Buy everything at once, or mix the tins together in a bucket before you start.

Questions people ask

How much paint do I need for a room?

Add up the wall area, take off the doors and windows, multiply by the number of coats and divide by the spread rate on the tin. The calculator does exactly that, adds a little for waste, and tells you which tins to buy.

How many coats of paint do I need?

Two is usual for walls and ceilings. Allow three when you're covering a strong colour or going from dark to light, and add a mist coat first on new plaster.

Should I include the ceiling?

Only if you're painting it. Switch on Paint the ceilings too and it's worked out separately, so you can buy a different paint for it.

Why is the spread rate lower than the one on my tin?

Manufacturers measure coverage on ideal surfaces. Real walls have texture, filler and porous patches, so the calculator starts from a more cautious figure. If you trust your tin's rate, type it in.

What if my room isn't a rectangle?

Choose Wall area for that room and enter the total area of its walls, doors and windows included: measure each wall's width by its height and add them up. The calculator takes the doors and windows off itself.

Does it work in feet and gallons?

Yes. Switch to imperial and type measurements in feet; spread rates are shown in square feet per UK gallon. Tins are still listed as sold, in litres.