Paint Calculator: How Much Paint Do I Need

It treats the room as a box and adds up the four walls: 2 times length plus width, all multiplied by the wall height. That gives the gross area before openings are removed. If you already know your wall area, you can approximate a rectangle whose perimeter matches it.

The default is 350 square feet per coat on smooth, primed walls. Rough, porous, textured or unprimed surfaces drink more paint, so lower the Coverage per gallon figure to match what the can states for your finish.

Two coats is standard for an even, durable finish and is the default here. One coat can work over a similar existing color, while a dramatic color change often needs a tinted primer plus two finish coats.

Each door removes 21 square feet and each window removes 15 square feet from the paintable area. These are typical averages. If your openings are unusually large, subtract an extra window or door to compensate.

Paint is sold in whole gallons and quarts, so the tool rounds the raw gallon figure up to the next whole can. That leftover paint is also useful later for touch ups after nicks and scuffs.

No, the estimate is walls only. To include a ceiling, treat it as a separate rectangle of length times width and run the numbers again, or add that area to a wall by adjusting your dimensions. Trim uses so little paint it is usually bought separately.

The liters figure simply converts the whole gallons you need using 3.785411784 liters per US gallon, so shoppers buying metric tins have a direct reference. It is derived from the rounded gallon count, not the raw area.

Yes. If the doors and windows you enter add up to more than the gross wall area, the paintable area floors at zero rather than going negative, and the paint needed becomes zero gallons.

No. All of the arithmetic happens locally in your browser, so your room measurements never leave your device and the tool keeps working offline.