Paint Coverage Calculator
Work out how much paint you need for a room, how many tins to buy, and an estimated cost, based on your wall area, coats and paint type.
Area Breakdown
Paint Needed by Number of Coats
Paint Coverage Calculator: How Much Paint Do I Need?
Our Paint Coverage Calculator helps you work out exactly how much paint to buy for a room, based on its dimensions, the number of coats you plan to apply, and the type of paint you’re using. Enter your room size (or a wall area you’ve already measured), deduct doors and windows, and get an estimate of the litres and tins required — plus an optional cost estimate.
How to Use This Calculator
- Choose how to enter your area – use room dimensions (length, width, height) or enter a wall area you’ve already measured.
- Decide whether to include the ceiling – if you’re painting the ceiling too, add it in with the room dimensions option.
- Enter doors and windows to exclude – these reduce the area that actually needs paint.
- Select a paint type – this sets a typical coverage rate, which you can adjust to match the figure on your tin.
- Choose the number of coats – most walls need two coats for even coverage, especially over a colour change.
- Pick a tin size – see how many tins to buy and how much paint, if any, you’ll have left over.
- Click Calculate Paint Needed to see your results.
Typical Paint Coverage Rates
Coverage varies by brand, colour and the porosity of the surface you’re painting. These are typical starting points for a smooth, previously painted surface — always check the specific figure printed on your tin.
| Paint Type | Typical Coverage | Notes |
|---|---|---|
| Emulsion (walls/ceiling) | ~12 m²/litre | Lower on unpainted plaster or dark-to-light colour changes |
| Gloss / Satinwood | ~16 m²/litre | For wood and metal trim, doors and skirting |
| Masonry Paint | ~6 m²/litre | Textured exterior surfaces reduce coverage further |
| Textured/Woodchip Cover-Up | ~8 m²/litre | Thicker, higher-build paint for uneven surfaces |
| Primer/Undercoat | ~10 m²/litre | Bare or very absorbent surfaces may need more |
How Many Coats Do I Need?
- One coat is sometimes enough for a like-for-like colour refresh over a sound, similar-coloured surface, though results can look patchy.
- Two coats is the standard recommendation for most emulsion work, giving even coverage and a consistent finish.
- Three coats may be needed for strong colour changes (for example, going from a dark colour to white), or for very porous new plaster.
Standard Door & Window Sizes
If you don’t know the exact size of your doors and windows, these typical UK figures are a reasonable starting point:
| Item | Typical Size |
|---|---|
| Standard internal door | ~1.5 m² (1.98m × 0.76m) |
| Standard window | ~1.5 m² (varies considerably by property) |
Tips for Buying the Right Amount of Paint
- Round up, not down: Running out mid-wall can leave a visible join if you have to wait for more paint or if the batch/shade varies slightly.
- Check the batch number: If buying more than one tin, try to buy them together, as very slight colour variation can occur between batches.
- New plaster needs more paint: Bare or freshly plastered walls are porous and will need a mist coat (diluted first coat) plus extra full coats.
- Dark-to-light colour changes need more coats: Budget for 3 coats when covering a strong existing colour with a much lighter one.
- Keep leftover paint: A small amount of spare paint, stored in a sealed container, is useful for future touch-ups and will match the batch.
Frequently Asked Questions
How much paint do I need for an average bedroom?
A typical UK box bedroom (around 3m x 3.5m with 2.4m ceilings) has roughly 31.2 m2 of wall area before deducting doors and windows. At a typical emulsion coverage of 12 m2/litre with two coats, that’s approximately 5.2 litres of paint before any door and window deductions, so two 2.5-litre tins (5 litres) would not quite be enough on their own. Use the calculator above with your own room and opening sizes for an exact figure.
Do I need to paint the ceiling separately?
Ceilings are usually painted with a flat white emulsion, which may have a different coverage rate to your wall colour. If you’re using the same paint for both, tick “include ceiling” in this calculator to add that area to your total. If you’re using a separate ceiling paint, it’s more accurate to run the calculation twice.
Why do I need more paint for a colour change?
Covering a dark colour with a lighter one (or vice versa) typically needs an extra coat compared with a like-for-like refresh, because the underlying colour can show through. Budgeting for three coats is common practice for significant colour changes.
Should I buy extra paint for touch-ups?
It’s common practice to round up to the next whole tin and keep any leftover paint, sealed and labelled, for future touch-ups and scuffs. This calculator shows how much spare paint you’ll have after rounding up to your chosen tin size.
Does a mist coat on new plaster use more paint?
Yes. New or bare plaster is porous and typically needs a diluted “mist coat” first, thinned according to the paint manufacturer’s instructions, followed by two full coats. This calculator’s coverage rate assumes a previously painted surface, so for bare plaster use a lower coverage rate (fewer m2 per litre) or account for an additional coat to reflect the extra paint absorbed.
How accurate is this calculator?
This calculator gives an illustrative estimate based on the figures you enter. Actual paint usage depends on your painting technique, the specific product, wall texture and colour change, so always check the coverage rate on your chosen tin and buy with a small margin for error.