Buying paint can feel like a guessing game. Too little, and you are halfway through the job when you realise you need another tin. Too much, and you are left with paint sitting in the shed for years.
The good news is that working out how much paint you need is fairly simple once you know what to measure.
Whether you are painting a feature wall, refreshing a bedroom, tackling the hallway or touching up woodwork, this guide will help you estimate how much paint to buy before you start.
The simple paint calculation
To work out how much paint you need, use this basic formula:
Surface area x number of coats ÷ paint coverage = litres of paint needed
That might sound a bit technical, but it breaks down into three easy steps:
- Measure the area you want to paint
- Multiply it by the number of coats needed
- Divide it by the coverage shown on the paint tin
Most paint tins will tell you how many square metres one litre should cover. This is usually shown as something like 12m² per litre, although it can vary depending on the paint, finish and surface.
Step 1: Measure the area
Start by measuring the height and width of each wall or surface you want to paint.
For each wall, multiply:
Height x width = square metres
For example, if a wall is 2.4 metres high and 3 metres wide:
2.4 x 3 = 7.2m²
Do this for each wall, then add the totals together.
If you are painting a full room, measure all four walls. If you are painting one feature wall, you only need to measure that wall.
Step 2: Take away doors and windows
You do not usually need to paint over doors, windows or large fitted units, so you can deduct these from your total.
Use the same calculation:
Height x width = square metres
For example, if a window is 1.2 metres high and 1.5 metres wide:
1.2 x 1.5 = 1.8m²
Subtract this from your wall total.
You do not have to be perfect to the last centimetre. The aim is to get a sensible estimate, not a surveyor-level calculation.
Step 3: Allow for the number of coats
Most decorating jobs need two coats for an even finish, especially if you are changing colour, painting over a darker shade or using a durable finish in a busy room.
Once you know the area, multiply it by the number of coats.
For example:
A room has 32m² of wall area after deducting windows and doors.
If it needs two coats:
32m² x 2 = 64m² of paint coverage needed
Step 4: Check the coverage on the tin
Now check the paint tin or product information for the coverage rate.
If the paint covers 12m² per litre, divide your total coverage by 12.
Using the example above:
64 ÷ 12 = 5.3 litres
In this case, you would usually buy a little more than 5 litres, depending on tin sizes and how much spare you want for touch-ups.
A quick example
Let’s say you are painting a small bedroom.
The walls total 30m² after deducting the door and window.
You want two coats.
The paint covers 12m² per litre.
The calculation would be:
30 x 2 = 60m²
60 ÷ 12 = 5 litres
So, for this room, around 5 litres should be enough for the walls.
What if you are painting a feature wall?
Feature walls are much easier to calculate because you are usually only painting one wall.
Measure the height and width of the wall, multiply them together, then multiply by the number of coats.
For example:
A feature wall is 2.4 metres high and 3.5 metres wide.
2.4 x 3.5 = 8.4m²
For two coats:
8.4 x 2 = 16.8m²
If your paint covers 12m² per litre:
16.8 ÷ 12 = 1.4 litres
In this case, a 2.5 litre tin may be the practical choice, giving you enough paint for good coverage and a little left for future touch-ups.
What about woodwork?
Woodwork is a little different because you are often painting smaller areas such as skirting boards, doors, door frames, shelves or window boards.
For a single internal door, a small tin may be enough, depending on the paint and number of coats. For a room with skirting boards, door frames and other trim, it is worth measuring roughly or asking for advice before buying.
If you are painting woodwork, also check whether you need primer, undercoat or a specific finish such as satin, eggshell or gloss.
Why you should not rely on guesswork
Guessing can be tempting, especially if you are already in the shop and just want to get the job done. But a quick measurement can save you time, money and frustration.
Buying too little can mean stopping halfway through the job. It can also be awkward if you need more paint mixed later, as small differences can sometimes show, especially on large walls or areas with strong light.
Buying far too much is not ideal either. Leftover paint can be useful for touch-ups, but it still needs storing properly and may not last forever.
Things that can affect how much paint you need
The calculation gives you a good starting point, but a few things can change how much paint you actually use.
The surface
Fresh plaster, porous walls, rough surfaces and bare wood can absorb more paint. You may need a mist coat, primer or extra preparation before applying your finishing coats.
The colour change
Going from dark to light, or light to dark, may need more care and sometimes an extra coat. Strong colours can also need good preparation to get an even result.
The paint finish
Different finishes can cover differently. Matt, silk, satin, eggshell and gloss all behave slightly differently, depending on the surface and product.
The condition of the wall
Cracks, stains, marks and repaired patches may need filling, sanding, cleaning or priming before you paint.
How you apply it
Brushes and rollers use paint differently. The type of roller sleeve, the texture of the wall and how heavily the paint is applied can all affect coverage.
A quick paint estimator
If you do not have exact measurements, this rough guide may help:
Small touch-up
A tester pot or small amount of mixed paint may be enough for a small patch, depending on the surface and colour.
Feature wall
For one average feature wall, 1 to 2.5 litres is often enough, depending on wall size, coverage and the number of coats.
Small room
For a small room, around 2.5 litres may be enough for the walls if the room is compact and the colour change is not too dramatic.
Medium room
For a medium-sized room, around 5 litres is often a sensible starting point for walls.
Woodwork
For a door, skirting boards or trim, a smaller tin may be enough, but this depends on how much woodwork you are painting and whether primer or undercoat is needed.
These are only rough estimates. For a better answer, measure the area and check the coverage on the paint tin.
What to bring into Collins Hardware
If you are visiting us for paint, it helps to bring:
Room measurements
Wall height and width
The number of walls you are painting
A note of doors, windows or areas you will not paint
A colour reference if you want paint mixed
A photo of the room for context
Details of the surface you are painting
You do not need to have everything perfect. Even rough measurements are better than guessing.
Need your paint mixed?
If you already have a colour in mind, bring your reference into Collins Hardware and we can help with our paint mixing service.
A good colour reference could be an old paint tin, colour code, sample card, wallpaper, fabric, tile or another clean, solid sample. Photos can be useful for inspiration, but lighting and screen settings can change how a colour appears.
Do not forget the decorating essentials
Paint is only part of the job. Before you start, it is worth checking whether you also need:
Brushes
Rollers
Paint trays
Masking tape
Dust sheets
Filler
Sandpaper
Primer or undercoat
Cleaning cloths
Scrapers or preparation tools
Getting these before you start can save an annoying trip back out once the room is covered in dust sheets.
Visit Collins Hardware for paint and decorating advice
If you are not sure how much paint you need, pop into Collins Hardware in Pangbourne and speak to the team.
Bring your measurements, colour reference or a quick photo of the room, and we will help you choose the right amount of paint, the right finish and the decorating supplies you need for the job.
Whether you are painting one wall, refreshing a room or touching up tired woodwork, we are here to help you get started with confidence.