Paint Calculator

Enter your wall dimensions and painting details to estimate the paint and cans you need.

Walls

Number of doors

Number of windows

Number of coats

Coverage (m²/L, per coat)

Paint can size

Net paintable area

— m²

Paint needed

— L

Cans needed

— cans

GUIDE

Learn more

How the Paint Formula Works (With a Worked Example)

Basic formula: Net paintable area = (sum of length × height for every wall) − (number of doors × door area + number of windows × window area). Paint needed = net area × coats ÷ coverage. Example: two walls at 5m × 2.5m each (25 m² total), minus 1 door (2.0 m²) and 2 windows (1.5 m² each = 3.0 m²), gives a net area of 25 − 2.0 − 3.0 = 20 m². At 2 coats and a coverage rate of 10 m²/L, you need 20 × 2 ÷ 10 = 4.0 liters — one 18L pail is plenty. Add up every wall, subtract door/window area, multiply by coats, then divide by coverage to get an accurate estimate.

How Many Coats Do You Actually Need?

Two coats is the standard default for most jobs. If you're making a big color change — especially going from a dark wall to a light color, or covering a very different hue — one or two coats may not fully hide the old color, so you may need three coats or more. Repainting in a similar tone often only needs one or two coats. For new drywall or dramatic color shifts, applying a primer first improves hiding power and can reduce the number of finish coats you actually need, saving paint and money in the long run.

How to Avoid Paint Waste

When rounding up to whole cans, if the leftover amount looks excessive, consider adding a smaller supplemental can instead of jumping to the next size up, to reduce waste. That said, always keep a small amount of leftover paint for future touch-ups. The calculator's default coverage (10 m²/L, roughly 350-400 ft²/gal) is a typical average — check the coverage rate printed on your actual product's label and enter that value for a more precise result. Measuring your wall length and height accurately, and counting every door and window, helps you avoid over-ordering.

Frequently asked questions

Why do I need to subtract doors and windows from the wall area?

Doors and windows aren't painted, so subtracting their area from the total wall area gives you the actual surface you'll be covering, resulting in a more accurate paint estimate.

What if my paint can's actual coverage is different from the 10 m²/L default?

Check the coverage rate printed on your paint can's label (in m²/L or ft²/gal) and enter that number into the coverage field instead of the default. Coverage varies by product, surface texture, and color, so the label value is always more accurate.

Does this calculator include primer as a separate step?

No, this calculator only estimates the finish (topcoat) paint. If you need primer, calculate it separately using the primer's own coverage rate over the same net wall area.

How many coats are typically recommended for a color change?

Two coats usually work for similar tones, but going from a dark color to a light one (or a big hue change) often needs three or more coats due to reduced hiding power. Applying a primer first can reduce how many finish coats you need.