How much paint do I need? For most rooms, you can work it out in about five minutes with a tape measure and the number printed on the tin. You measure the wall area, take off the doors and windows, multiply by the number of coats, then divide by the spread rate. Below, you’ll see how it works for a typical bedroom, plus a table you can take to the shop.
Quick answer
Here’s the formula:
(Wall area minus doors and windows) x number of coats ÷ spread rate = litres
Spread rate is how many square metres one litre covers. You’ll find it on the tin or the product data sheet. Most interior jobs need two coats.
A 3 x 4 metre bedroom with standard walls needs about 4 litres of wall paint. The ceiling needs about 2 litres more. That’s a rough guide, so keep reading to see where the numbers come from.
How to measure a room in square metres
You only need a tape measure and a calculator. Start with the walls.
- Measure the total length of all walls. For a 3 x 4 metre room, that’s 14 metres.
- Measure the ceiling height. Many homes sit at 2.4 metres, but older Melbourne houses often run taller, so check yours.
- Multiply length by height. That’s your gross wall area.
- Measure each door and window, then subtract them.
A standard door is roughly 1.6 m² on one side. Small windows under 1 m² won’t change the answer much, so that you can skip them.
Don’t use the floor area. A 12 m² floor tells you nothing about how much wall you have.
Spread rate: how far a litre goes
Every paint has its own spread rate. Cheaper paints usually cover less. Premium paints usually cover more.
Dulux lists a theoretical spread rate of 16 m² per litre for Wash&Wear Low Sheen, and its data sheet recommends two coats. Notice the word “theoretical”. It’s measured under ideal conditions.
In a real house, you’ll often get less. Bare plasterboard, rough walls and dark colours over light ones all soak up more paint. Because of that, many painters plan for a slightly lower figure than the tin says. If your paint doesn’t list a rate, ask the shop or read the data sheet online.
Worked example: a 3 x 4 metre bedroom
Let’s use Dulux Wash&Wear Low Sheen at 16 m² per litre, with 2.4 metre walls, one door and one window.
| Step | Working | Result |
| Wall length | 3 + 4 + 3 + 4 | 14 m |
| Gross wall area | 14 x 2.4 | 33.6 m² |
| Door and window | 1.6 + 1.8 | 3.4 m² |
| Paintable area | 33.6 minus 3.4 | 30.2 m² |
| Two coats | 30.2 x 2 | 60.4 m² |
| Litres needed | 60.4 ÷ 16 | 3.8 L |
So, you’d buy one 4-litre tin. That leaves very little spare, though. If your walls soak up paint and you only get 12 m² per litre, the same room needs about 5 litres. In that case, a 4-litre tin plus a 1-litre tin is safer.
Ceilings, doors and trims
Ceilings are simple. The ceiling of a 3 x 4 metre room is 12 m². Two coats make 24 m², and 24 ÷ 16 gives 1.5 litres. A 2-litre tin does the job.
If you’re new to ceilings, our guide on how to paint a ceiling covers the technique and the tools.
Doors and skirting boards use less paint, but they add up. As a rough guide:
- A door has two sides, so count about 3.3 m² for both.
- Skirting around a 14 metre room, at about 12 cm high, comes to roughly 1.7 m².
- One litre of trim paint usually covers the skirting and a door or two with two coats.
Trim paint often spreads a little less than wall paint, so check the tin.
How much primer or undercoat to buy
Primer needs one coat, so the maths is easier. Divide the paintable area by the primer’s spread rate.
Say your primer covers 12 m² per litre. For our bedroom, 30.2 ÷ 12 gives about 2.5 litres. A 4-litre tin would cover it with some left over.
Primer spread rates vary a lot between products, so check the label before you buy. Not sure whether you need it at all? Our step by step guide on how to paint a room explains when primer matters.
Tin sizes and buying tips
Paint usually comes in 1, 2, 4, 10 and 15 litre tins. Larger tins often cost less per litre, so it can pay to round up to a 10-litre tin on bigger jobs.
Here’s a quick table for walls and ceilings. It assumes two coats, 2.4 metre ceilings, 16 m² per litre, and one door and one window.
| Room size | Paintable wall area | Wall paint needed | Buy | Ceiling paint | Buy |
| 3 x 3 m | 25.4 m² | 3.2 L | 4 L | 1.1 L | 2 L |
| 3 x 4 m | 30.2 m² | 3.8 L | 4 L | 1.5 L | 2 L |
| 4 x 4 m | 35.0 m² | 4.4 L | 4 L + 1 L | 2.0 L | 2 L |
| 4 x 5 m | 39.8 m² | 5.0 L | 4 L + 2 L | 2.5 L | 2 L + 1 L |
| 5 x 6 m | 49.4 m² | 6.2 L | 10 L or 4 L + 2 L + 1 L | 3.8 L | 4 L |
A few more tips:
- Buy all the paint at once. Tinted batches can differ slightly in colour.
- Mix tins of the same colour in one bucket before you start.
- Keep any leftover paint sealed for touch-ups.
Planning a feature wall? Work out its area on its own, since a 1 or 2 litre tin is often enough. Our feature wall ideas guide can help you choose colours and placement.
Painter’s tip: For a standard bedroom, we usually start with a 4 litre tin for the walls and a 2 litre tin for the ceiling. We’d rather have a little left over than stop halfway.
Common mistakes
Most shortfalls come from the same few slips.
- Forgetting the second coat. The formula needs it, so don’t skip that multiplication.
- Trusting the floor area. Wall area is what matters.
- Using the best-case spread rate. Rough or bare surfaces often cover less than the tin suggests.
- Using wall paint figures on other surfaces. Tile paint, for example, has its own spread rate and prep steps. We cover it in our recent post on how to paint tiles.
- Buying exactly what you need. A small buffer saves you a second trip.
Frequently asked questions
How much paint do I need for one room?
A bedroom usually needs 4 to 5 litres for the walls and 1.5 to 2 litres for the ceiling, with two coats. Larger rooms need more. Use the table above for a closer match.
How many square metres does a 4-litre tin cover?
At 16 m² per litre, a 4-litre tin covers about 64 m² in one coat, or 32 m² in two. If your paint spreads at 12 m² per litre, that drops to 48 m² and 24 m².
How much paint do I need for a ceiling?
Multiply the ceiling area by the number of coats, then divide by the spread rate. A 12 m² ceiling with two coats needs about 1.5 litres.
How much paint do I need per square metre?
At 16 m² per litre, one coat needs about 0.06 litres per square metre. Two coats need roughly 0.125 litres. Your own figure will depend on the paint and the surface.
Is it better to buy too much paint or too little?
A little too much is usually the better choice. Running out means a second trip, and a new batch can look slightly different. Leftover paint also helps with touch-ups later.
Rather have it painted for you?
Measuring, buying, and rolling two coats takes a weekend. If you’d rather skip it, our licensed and insured Melbourne painters can handle the whole job. We give free quotes after we inspect the property.
Contact NUW Pro Painting for a quote or call 0478 782 077.
