Start with the surfaces you will paint.
Write down every wall you plan to paint. Measure its width and height, then multiply the two numbers to find the area. Add the walls together. If your room has different wall heights, record each wall separately rather than using one average.Step 02
Keep the ceiling separate.
For a rectangular ceiling, multiply room length by room width. Keep that area separate if the ceiling needs a different paint, finish or number of coats. The same approach works for trim: record it as its own part of the project.
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Account for openings.
Measure doors and windows that will not be painted and record their combined area. Subtracting openings gives a closer surface estimate, but small differences may disappear when you round your purchase to the available can sizes.Step 04
Check the paint, then calculate.
Use the coverage stated on the paint label and the number of coats planned for your surface. Coverage can vary with texture, absorbency, color changes and application. A calculator is a starting point; the product instructions remain important.