Calculating how much paint you need

In order to calculate how much paint you need to paint a room, house, or an exterior surface, you need to either know the measurements by plan, or have a long measurement tape ready (10 or 20 meter / 33 or 65 foot long is advised) before you can use this paint calculator. If you are painting an interior surface, you need to know the room’s width, length and height. Rooms with non-rectangular layout can be approximated to rectangles. If you need to paint a ceiling or external wall, switch to “External” in the calculator and just enter the total width and height of the wall (or width and length instead, for a ceiling).

Usually the room or exterior will have openings for windows and doors which need to be excluded from the total surface area. Accurate measurement of the windows is important, especially if there are many of them. Our tool only supports one set of window dimensions, so if you have a room with multiple windows of highly different dimensions, you’d need to use the average. In this how much paint do I need calculator door dimensions are assumed to be close to construction standards (200mm by 90mm).

The other important thing to consider is the paint coverage efficiency (a.k.a. spreading rate): how many square meters or square feet you can cover with a litre or gallon of the paint. Manufacturers usually provide this information on the product label. Different paints and primers have different coverage capacity so make sure you use the right number as input. You’d want to allow for a lower efficiency in case the surface is not smooth. More coarse surfaces require more paint to cover.

Finally, if you enter the paint price per gallon or per litre the output will include the total price of the paint required. The tool rounds up to the closest gallon or litre, but you might want to order more paint just to be on the safe side.

Georgiev G.Z., “Paint Calculator”, [online] Available at: URL [Accessed Date: 05 Jul, 2022].