Paint calculator
Estimate paint for a room or known surface: walls, ceiling, openings, coats, coverage, waste and container sizes.
Paint calculation
Measure the actual area to paint, deduct openings and get litres plus a suggested container combination.
Doors and windows
Add the doors and windows to deduct.
Purchase settings
In litres, separated by commas. Example: 10, 5, 2.5, 1.
Purchase suggestion
Suggestion based on the available sizes, favouring the smallest purchased volume that covers the need.
Theoretical requirement
Purchased volume
Surplus
Calculation details
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How does this tool work?
The paint calculator estimates the net area to cover, the litres needed and a practical combination of tins. It can start from the full dimensions of a room or from an area you have already measured, deduct doors and windows, include the ceiling, and apply several coats and a waste allowance.
For a room, the engine calculates the four walls as 2 × (length + width) × height and adds length × width for the ceiling when you choose to paint it.
Each door or window is deducted as width × height × quantity. In known-area mode, the area you enter is used as it is, so it should already be net of openings.
The net area is multiplied by the number of coats and divided by the coverage in m²/L shown on the tin. The waste allowance is then added to these theoretical litres.
Finally, the calculator looks for the combination of available tin sizes that covers the requirement with the smallest purchased volume, then shows the surplus.
Example: covering 42 m² with paint rated at 10 m²/L for two coats requires 8.4 L before waste. Substrate porosity, application method and the real product coverage can increase consumption.
How to use this tool
Choose the method
Room dimensions or a known area.
Deduct the openings
Add as many doors and windows as needed, with their quantity.
Describe your paint
Number of coats and coverage in m²/L from the product data.
Plan the purchase
Adjust the list of tin sizes to those actually available.
Paint quantity formulas
The coverage printed on the tin remains the reference value.
Room walls
A = 2 × (length + width) × height
Area of the four walls.
Net area
net A = walls + ceiling − openings
The doors and windows you enter are removed.
Litres
L = net area × coats ÷ coverage
The chosen allowance is then added.
Hiding power depends on the substrate, the colour, the preparation and the product. Use the manufacturer’s coverage and adapt the number of coats to your job.
Use cases
Repainting a room
Work out walls, ceiling, doors and windows from the room’s dimensions.
Area already measured
Enter the square metres directly when you already know the area to paint, for example a single feature wall.
Planning the purchase
Turn the litres required into a combination of the tin sizes your shop actually sells.
Examples
Walls of a 4 × 3 m bedroom
The walls cover 2 × (4 + 3) × 2.5 = 35 m², minus 3.28 m² of openings. 31.72 × 2 ÷ 10 = 6.34 L, plus 10% = 6.98 L: 7 L bought, leaving 0.02 L spare.
Input
Height 2.5 m · door 0.90 × 2.04 m · window 1.20 × 1.20 m · 2 coats · 10 m²/L · 10% allowanceResult
Net area 31.72 m²; 6.34 L in theory; 6.98 L required; one 5 L tin + two 1 L tinsSame bedroom including the ceiling
The ceiling adds 4 × 3 = 12 m². The suggested combination is a single 10 L tin, with 0.38 L left over.
Input
Same dimensions and openings · ceiling painted · 2 coats · 10 m²/L · 10% allowanceResult
Net area 43.72 m²; 8.74 L in theory; 9.62 L required; one 10 L tinTips and best practices
- Read the coverage on the tin: a paint rated at 10 m²/L can cover less on a porous or textured surface.
- A suitable primer or undercoat can reduce how much finishing paint you need, especially on new plaster.
- You do not always need to deduct very small openings: losses in the roller tray and when cutting in can offset them.
Sources and references
Frequently asked questions
How do I work out how many litres of paint I need?
Multiply the net area by the number of coats, then divide by the coverage in m²/L. Add an allowance suited to the surface: 31.72 m² × 2 coats ÷ 10 m²/L gives 6.34 L before the allowance.
Should doors and windows be deducted?
For an accurate estimate, yes. The calculator lets you add several openings with their quantity. If you enter a known area, deduct them before typing it in.
Which coverage figure should I use?
Use the value given by the manufacturer of the paint you have chosen first. A generic figure is only a starting point.
Why add a waste allowance?
It covers differences in how much the surface absorbs, losses during application and small touch-ups.
Do I have to follow the suggested tins?
No. The suggestion only turns litres into practical sizes. Edit the list to match the sizes actually on sale; it minimises volume, not price.
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