Paint Calculator

About Paint Calculator

Calculate paint for 4 walls. Subtract ~10% for windows and doors. Most rooms need 2 coats.

How to use this calculator

1. Measure the room length, width, and height.
2. Measure the area of doors and windows you want to exclude.
3. Enter the paint coverage listed on the paint can.
4. Calculate the wall area, subtract openings, then divide by coverage.

The formula explained

• \(\text{length}\) = room length
• \(\text{width}\) = room width
• \(\text{height}\) = room height
• \(\text{openings}\) = total area of doors and windows to subtract
• \(\text{coverage}\) = area covered by one unit of paint, usually per gallon or per liter
• \(\text{paint needed}\) = amount of paint required

Step by step method

1. Find the wall area by adding the two pairs of opposite walls: 2 times length times height, plus 2 times width times height.
2. Subtract the area of doors and windows so you do not count surfaces that will not be painted.
3. Divide the remaining area by the paint coverage to find how much paint you need.
4. If the result is not a whole number, round up so you have enough paint.

Worked example

Suppose you are painting a bedroom that is 4 m long, 3 m wide, and 2.5 m high, with 3 m of openings, and one liter covers 10 square meters.

1. Compute the wall area: \(2(4 \cdot 2.5 + 3 \cdot 2.5) = 2(10 + 7.5) = 35\) square meters.
2. Subtract openings: \(35 - 3 = 32\) square meters to paint.
3. Divide by coverage: \(32 \div 10 = 3.2\) liters.

Tips and common mistakes

• Measure wall height carefully, especially if the ceiling is sloped or uneven.
• Check whether the calculator includes one coat or two coats, because two coats roughly double the paint needed.
• Use the coverage value from the specific paint can, since different paints cover different amounts.
• Do not forget to subtract large doors and windows if the tool asks for openings.

Frequently asked questions