How much paint do you need?

What This Paint Calculator Does

This paint calculator estimates how many liters of paint you need to cover a wall or room. You enter the total wall area, the number of coats you plan to apply, and the coverage rating of your paint (square meters per liter). The calculator returns the liters required and adds a small buffer so you don't run short mid-project.

It's built for DIY painters, renters refreshing a room, and tradespeople pricing a job. Instead of guessing or over-buying, you get a quick, repeatable number you can take to the paint store.

How It Works: The Coverage Formula

The calculation is straightforward. Paint coverage is usually printed on the can, often 10 to 14 m² per liter for a single coat on a smooth, primed surface.

The formula is:

liters = (wall area x number of coats) / coverage per liter

Because real surfaces absorb extra paint and some is lost to rollers, trays, and trim, the calculator buys roughly 10% extra:

liters to buy = liters x 1.10

Worked Example With Real Numbers

Say you're painting a room with 60 m² of wall area, applying 2 coats, with a paint rated at 12 m² per liter.

Plugging in the numbers: liters = (60 x 2) / 12 = 120 / 12 = 10 liters.

Adding the 10% buffer: 10 x 1.10 = 11 liters. You'd buy about 11 liters, which in practice means three 2.5-liter cans plus one extra, or two 5-liter cans with a little to spare for touch-ups.

Measuring Wall Area Correctly

Accurate area is the biggest factor in your result. Measure each wall's width and height, multiply them, and add the walls together.

A few practical adjustments:

• Wall area = wall length x ceiling height for each wall.
• Subtract large openings like doors (roughly 2 m² each) and big windows (1 to 1.5 m² each).
• For small windows or trim, it's fine to leave them in as part of your safety margin.
• Painting the ceiling too? Add floor area (length x width) as a separate surface.

Factors That Change How Much Paint You Need

Coverage is an ideal figure from the manufacturer. Several real-world conditions push your actual usage up or down.

• Surface texture: rough plaster, masonry, or textured walls soak up more paint than smooth drywall.
• Color change: covering a dark wall with a light color, or vice versa, often needs an extra coat.
• Bare or porous surfaces: new drywall and fresh plaster drink the first coat, so prime first or expect lower coverage.
• Application method: rollers and brushes waste more paint than sprayers, but sprayers can use more overall.
• Paint type: thick, matte, and premium paints sometimes cover better per coat than cheap or glossy ones.

Common Mistakes and Practical Tips

The most frequent errors are forgetting to multiply by the number of coats and trusting the coverage rating as a guarantee rather than a best case. Both lead to running out partway through.

• Buy all your paint at once and check the batch number so colors match exactly.
• Keep the leftover from the 10% buffer for future touch-ups; store it sealed and labeled.
• Always plan for at least two coats unless you're applying the same color over a sound, similar surface.
• If you're priming, calculate primer separately using the same formula and its own coverage rating.
• When in doubt, round up to the next full can rather than under-buying.