YardCompute / Project Guides / Paint Calculation

How to Calculate Paint for a Room

A paint estimate starts with wall area and then adjusts for doors, windows, the number of coats, the paint's stated coverage, and a practical allowance. Product coverage is the most important product-specific input, so check the label for the paint you plan to use.

1. Calculate gross wall area

For a simple room, calculate each wall's width × height and add the results. If all four walls are the same height and the room is rectangular, perimeter × wall height can also be used.

2. Subtract major openings

Measure doors and windows that will not receive the same wall paint. Calculate each opening's width × height and subtract the total opening area from the gross wall area.

3. Account for coats

Multiply the net wall area by the number of coats. For example, 600 square feet of net wall area with two coats creates 1,200 square feet of paint coverage to plan for.

4. Divide by product coverage

Divide the total paintable coverage by the coverage stated on the product label.

Gallons = paintable area × coats ÷ coverage per gallon

If the calculation gives 3.2 gallons, the purchase quantity may need to be rounded up based on the container sizes available and the product system you are using.

Why real coverage can differ

Coverage can change with surface texture, porosity, color changes, application method, primer, and the condition of the wall. A planning allowance can help, but it should not replace the manufacturer's coverage guidance.

Common mistakes

• Using floor area as if it were wall area.
• Forgetting doors and windows.
• Ignoring the number of coats.
• Using a generic coverage value instead of the paint label.
• Assuming one gallon always covers the same area on every surface.

Use the Paint Calculator

Use the YardCompute Paint Calculator to estimate paint from wall dimensions, openings, coats, product coverage, and an adjustable waste allowance.

FAQ

How much wall area does a gallon of paint cover?

Coverage varies by product. Use the coverage printed on the specific paint label rather than relying on a generic number.

Should I subtract windows and doors?

Yes, when those surfaces will not receive the same wall paint. Large openings can materially change the estimate.

How many coats should I use?

Follow the paint manufacturer's directions and the needs of the surface. The calculator lets you enter the number of coats rather than assuming one universal value.