Paint Calculator for a Room
Estimate gallons of paint for the walls and ceiling of a room, with allowances for doors and windows.
Calculator
| Gallons to buy (whole) | 2 gal |
|---|---|
| Paintable wall area | 312 ft² |
| Extra for the ceiling | 0.82 gal |
How it is calculated
Walls = 2 × (12 + 12) × 8 ft = 384 sq ft, minus 2 doors (21 sq ft each) and 2 windows (15 sq ft each) = 312 sq ft. At 350 sq ft per gallon and 2 coats: 1.78 gallons.
About this calculator
Paint quantity depends on the wall area, the number of coats and the paint's coverage. A gallon typically covers roughly 350 to 400 square feet per coat on a smooth, previously painted wall; rough, porous or very dark surfaces need more.
This calculator subtracts typical door and window openings (about 21 and 15 sq ft), multiplies by the number of coats and divides by 350 sq ft per gallon. If the coverage printed on your can differs, trust the can: a higher number means you need less paint.
Worked examples
| Project | Gallons for the walls | Rough cost |
|---|---|---|
| a 12x12 ft room with 8 ft ceilings | 1.78 gal | $60.00 – $140 |
| a 10x12 ft room with 8 ft ceilings | 1.81 gal | $60.00 – $140 |
| a 14x16 ft room with 9 ft ceilings | 2.59 gal | $90.00 – $210 |
| a 20x20 ft room with 10 ft ceilings | 3.99 gal | $120 – $280 |
Buying notes
- Buy a little extra for touch-ups, and label leftovers with the room and color.
- Primer on new drywall, stains or big color changes can save a coat of finish paint.
- Ceilings usually take a different paint; use the ceiling paint calculator for them.
Quick answers by size
Click a size for the exact quantity and cost.
How to measure and use this calculator
- Measure the room's length, width and ceiling height.
- Count doors and windows; the calculator subtracts typical sizes.
- Set the number of coats, usually two when changing color.
- Buy a little extra for touch-ups.
Common mistakes
- Skipping primer on bare drywall or dark colors, which costs coats.
- Forgetting that textured walls drink more paint.
- Buying different batches; mix cans together to keep color consistent.
Tips
- One gallon typically covers about 350–400 sq ft per coat; porous or dark surfaces take more.
- Two coats are standard when changing colors.
- Buy a bit extra for touch-ups, and keep the leftover labeled with the room and date.
Frequently asked questions
How much paint do I need for a 12x12 room?
About 1.8 gallons for two coats on the walls with standard 8 ft ceilings, plus about 0.8 gallons if you also paint the ceiling.
Do I need two coats of paint?
Often when changing color or painting over a dark color. One coat can be enough over a similar color with good-coverage paint, but two coats usually look more even.
What if my ceilings are higher than 8 feet?
Enter the real ceiling height. The calculator scales the wall area, so taller rooms get a proportionally larger amount.