How to Estimate Paint for a Room
Buying the right amount of paint means one trip to the store and leftover for touch-ups. This guide walks through measuring walls, accounting for coats, and converting area to gallons.
Ready to run the numbers? Use our Paint Calculator or the Paint Cost Calculator to get an instant material estimate.
1. Measure the paintable wall area
For each wall, multiply height × width in feet and add the walls together. Then subtract openings you will not paint — doors (about 21 ft² each), windows (about 15 ft² each), and large built-ins. If you are painting the ceiling, add the room’s length × width as a separate area.
A 12×12 ft room with 8 ft walls: 4 walls × (12 × 8) = 384 ft², minus one door (21) and two windows (30) = 333 ft² of paintable wall.
2. Account for coats and coverage
Most rooms need two coats for an even finish, especially over a different color or on new drywall. One gallon of standard interior paint covers about 350–400 ft² per coat — check your specific can, since coverage varies by brand and finish.
Source: Standard interior paint coverage ≈ 350 ft²/gal on smooth, primed walls.
333 ft² of wall, 2 coats, 350 ft²/gal: 333 × 2 ÷ 350 = 1.9 → 2 gallons. Round up so you have leftover for touch-ups.
3. Plan primer and supplies
- Use primer on new drywall, repairs, or a dramatic color change.
- Budget for trim paint separately — a gallon covers a typical room’s trim.
- Ceiling paint is usually flat; wall paint is eggshell or satin.
- Buy all paint at once and mix the gallons together for consistent color.
4. Estimate the cost
Multiply gallons by your price per gallon. Paint prices vary widely by brand and line, so enter your actual quoted price for the most accurate total. Add brushes, rollers, drop cloths, and tape as a separate line.
Frequently asked questions
How much paint do I need for a 12×12 room?
A 12×12 ft room with 8 ft walls has about 333 ft² of paintable wall after one door and two windows. Two coats at 350 ft²/gal needs about 2 gallons.
How many square feet does a gallon of paint cover?
About 350–400 ft² per coat on smooth, primed walls. Coverage drops on rough surfaces, dark colors over light, or with a thick roller nap — check your can for the exact number.
Do I need two coats of paint?
Usually yes. Two coats give an even finish and full color depth, especially over a different color or on new drywall. A single coat can work for a same-color refresh.
Calculators for this guide
Put these numbers to work with the free calculators referenced above.