Paint Calculator

Estimate how much paint you need. Enter walls by width × height or as total surface area, subtract doors and windows, set coats, coverage, waste and container size in metric or imperial units, and see paint required and whole containers to buy.

Calculators Runs client-side Free to use

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About the Paint Calculator

Paint Calculator estimates the amount of paint for a room or project. Enter each wall as width × height with a quantity, or enter total surface areas directly, then list doors, windows and other openings to subtract. Set the number of coats, the coverage printed on your paint (square metres per litre or square feet per US gallon), an optional waste percentage and the size of the container you plan to buy.

The results show the gross area, the area of openings, the net area to paint, the paint needed before and after waste, and the number of whole containers to buy, with a step-by-step calculation. The tool works in metric (metres and litres) or imperial (feet and US gallons) units and does not recommend products or prices. Actual paint use varies with the surface, the paint type and the application method, so treat the result as an estimate.

How to use

Choose metric or imperial units.
Enter each wall’s width and height (or switch to total surface area).
Add doors, windows and other openings to subtract.
Enter coats, coverage from the paint label, waste % and container size.
Click Calculate, then copy or download the summary.

Key features

Wall width × height or total surface area modes.
Multiple walls or surfaces with quantities.
Doors, windows and openings subtracted.
Coats, coverage, waste allowance and container size inputs.
Paint before and after waste, plus whole containers to buy.
Metric and US imperial units, with copy, download and Reset.

Best practices

Use the spreading rate from your paint’s label or technical data sheet.
Plan two coats for colour changes and new plaster or drywall.
Add 10–15% waste for textured, porous or previously unpainted surfaces.
Measure openings accurately; small windows add up across a whole house.
Buy all paint from the same batch to avoid colour differences.

Benefits

Avoid buying too little or far too much paint.
Clear breakdown you can check by hand.
Works for single walls, rooms or whole projects.
Private, free and works offline once loaded.

Frequently asked questions

How much paint do I need for a room?

Multiply the net wall area (walls minus doors and windows) by the number of coats and divide by the paint’s coverage per litre or gallon. The calculator does this and rounds up to whole containers.

Where do I find the coverage figure?

It is printed on the paint container or its data sheet, usually as m² per litre or sq ft per gallon. Many wall paints cover roughly 10–12 m² per litre per coat, but always use your product’s figure.

Why might I need more paint than estimated?

Rough, porous or textured surfaces, strong colour changes, primer requirements and spraying all increase paint use. Actual use varies by surface, paint type and application method.

Does it use US or UK gallons?

Imperial mode uses US gallons (3.785411784 litres). If your paint is sold in litres, use metric mode.

Can I calculate ceilings too?

Yes. Add the ceiling as another wall using its length and width, or switch to total surface area and enter its area.

Does it recommend paint brands or prices?

No. It only estimates quantities from the figures you enter.

Is my data saved or uploaded?

No. Every calculation runs in your browser. Nothing you type is sent to a server or saved in browser storage, and Reset clears it from the page.