Short answer: One gallon of paint covers about 350 square feet, so a gallon paints about 175 square feet with two coats. A 12 ft by 14 ft room with 8 ft walls needs about 2.1 gallons for two coats on the walls, so buy 3 gallons.
| Room size | Wall area to paint | Gallons to buy |
|---|---|---|
| 10 x 10 ft | 270 sq ft | 2 |
| 12 x 12 ft | 334 sq ft | 2 |
| 12 x 14 ft | 366 sq ft | 3 |
| 14 x 16 ft | 430 sq ft | 3 |
| 16 x 20 ft | 526 sq ft | 4 |
How the amount is worked out
Add up the room perimeter and multiply by the wall height, then subtract the doors and windows. Multiply by the number of coats and divide by the coverage on the can, which is often between 300 and 400 square feet per gallon. Round up to whole gallons.
Rough or porous walls soak up more paint, and a big color change often needs a primer coat first.
Ceilings and trim
The table covers the walls only. A ceiling adds its own area, which is length times width. Trim and doors use little paint, and are often done from a leftover quarter of a gallon.
Worked example
A room 12 ft by 14 ft with 8 ft walls has 416 sq ft of wall. Removing one door and two windows leaves 366 sq ft. Two coats is 732 sq ft, and at 350 sq ft per gallon that is 2.09 gallons, so buy 3.
Use the Paint CalculatorEnter your own measurements and get an exact amount.
Frequently asked questions
How many coats of paint do I need?
Two coats is the normal rule. One coat can be enough when repainting a similar color with a quality paint.
How much paint do I need for a 12 by 12 room?
For the walls with two coats, buy 2 gallons with one door and two windows. The calculator gives the exact amount for your own openings.
Does the coverage on the can always apply?
It is a best case on smooth, primed walls. Textured or dark surfaces take more paint.
Related calculators
Figures are typical planning values. Material sizes, densities and local requirements vary, so confirm with your supplier before ordering.
Last updated October 11, 2026.