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Paint Coverage Calculator

Work out how much paint a room needs and which tins to buy, with doors, windows, and coats.

  • paint
  • coverage
  • litres
  • gallons
  • coats
  • room
  • walls
  • ceiling
  • canada

About Paint Coverage Calculator

Buying paint is a guessing game without the numbers: too little and you're back at the store mid-job hoping the next tin matches the batch; too much and you've got half-used cans cluttering the shed. This calculator turns a room's dimensions into the litres or gallons you actually need, then tells you which combination of standard tins to buy to cover it.

It measures the way you paint a room — wall area from the perimeter and ceiling height, with the option to add the ceiling — and lets you knock off the doors and windows you won't be painting. Factor in the number of coats and your paint's spread rate, and it converts the result into Canadian 1 L, 4 L, and 18.9 L tins (or quarts, gallons, and 5-gallon pails in imperial), rounding up to whole containers.

How to use

Choose metric or imperial and enter the room's length, width, and ceiling height. Tick "include the ceiling" if you're painting it, then set how many doors and windows to deduct — the tool uses standard sizes for each. Enter the number of coats (two is typical) and your paint's spread rate; the label on the tin quotes this, and the default suits a smooth, previously-painted wall.

The headline shows total paint required, with the other unit beneath it, and the "suggested tins" card breaks that into whole containers to buy. Bare drywall, render, and bold colour changes need more, so round up rather than down, and keep a touch-up tin from the same batch so the shade matches later.

Frequently asked questions

  • How much paint do I need for a room?

    Work out the wall area — the room's perimeter times the ceiling height — add the ceiling if you're painting it, then subtract the doors and windows. Multiply by the number of coats and divide by the paint's spread rate. A typical 4 × 3 m room with 2.4 m ceilings has about 34 m² of wall, so two coats at 12 m²/L is roughly 5.6 litres. The calculator does all of this and rounds it into tins for you.

  • How many coats of paint should I apply?

    Two coats is standard for a durable, even finish and the default here. One coat may do for a like-for-like refresh in a similar colour, while a big colour change — especially light over dark, or any colour over bare drywall — often needs a primer plus two coats, or three coats of self-priming paint. Each coat multiplies the paint required, so set the number to match your job.

  • What is paint spread rate and what should I use?

    Spread rate is how much area a litre (or gallon) covers in one coat — the tin quotes it, often around 10–13 m²/L (roughly 350–450 ft²/gal) for a smooth interior wall. Rough, textured, or porous surfaces like bare drywall, render, and timber soak up more, lowering the effective rate. If you're unsure, use the figure on the tin and round your order up.

  • Should I subtract doors and windows?

    Yes — they're a meaningful chunk of a wall you won't paint. This tool deducts a standard 1.9 m² per door (about 2.1 × 0.9 m) and 1.2 m² per window (about 1.2 × 1.0 m). If your openings are much larger or smaller, the result is a close approximation; for an oversized picture window or patio door you may want to allow a little less paint than the headline suggests.

  • What tin sizes does it recommend?

    In metric it uses the common Canadian retail sizes — 1 L, 4 L, and the 18.9 L pail — and in imperial the US quart, gallon, and 5-gallon pail. It fills largest-first so you buy the fewest containers with the least leftover, always rounding up to whole tins since you can't buy a partial one. Buy all tins of the same colour from one batch so the shade is consistent.

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