Paint guide
How much paint do I need?
The reliable starting point is wall area, not floor area. Measure the room perimeter, multiply by wall height, subtract openings, then multiply by coats.
Start with wall area, not floor area
Floor area is useful for carpet and tile, but it is a poor shortcut for paint. A small room with tall walls can need more paint than a larger room with low walls. The most reliable first estimate is the total wall surface that will actually be painted.
Paintable wall area = 2 x (length + width) x wall height - doors and windows. After that, multiply by the number of coats. This gives the total coverage you need to buy.
Worked example
A 12 ft by 10 ft room with 8 ft walls has a perimeter of 44 ft. Multiply 44 by 8 and the walls have 352 sq ft of surface before openings. If doors and windows total 45 sq ft, the paintable wall area is 307 sq ft.
For two coats, the project needs coverage for 614 sq ft. If the paint label says one gallon covers about 350 sq ft on a smooth wall, the math is 614 / 350 = 1.75 gallons. In practice, you would usually buy two gallons or the nearest larger container.
| Situation | Planning adjustment | Reason |
|---|---|---|
| Smooth wall, similar color | Use the label coverage | The surface is close to the ideal condition used for coverage estimates. |
| Dark color over light, or light over dark | Plan for primer or extra coat | Color changes often need more coverage to look even. |
| Fresh drywall or patched wall | Round up | Porous surfaces absorb more paint. |
| Textured plaster or brick | Use a lower coverage number | Rough surfaces add hidden area and absorb paint unevenly. |
Common mistakes
- Forgetting that two coats doubles the coverage requirement.
- Subtracting large windows but not accounting for trim or accent walls.
- Using the most optimistic coverage number from the paint label.
- Buying exactly the calculated amount and having no touch-up reserve.