Paint Calculator
Enter your room dimensions in feet, subtract doors and windows, and get an instant estimate of how many gallons of paint you need — plus a rough cost.
This calculator estimates how many gallons of paint you need for a room and gives you a rough dollar cost. Everything is in U.S. units — feet, inches, gallons, and dollars. Measure the length and width of the room, the wall height (8 ft is standard for most U.S. homes), and count the doors and windows you will not be painting.
Fill in the room details and press Calculate to see gallons of paint and an estimated cost.
How the paint calculator works
The math is simple, and it helps to see it so you can sanity-check the result:
- Wall area = 2 × (length + width) × wall height. For a 12 × 12 ft room with 8 ft walls that is 2 × 24 × 8 = 384 sq ft.
- Subtract openings you are not painting: 21 sq ft per door, 15 sq ft per window.
- Multiply by coats, then divide by 350 sq ft per gallon.
- Round up to the next whole or half gallon, because you cannot buy a partial can and you want a little left over for touch-ups.
Tips for a more accurate estimate
- New drywall and bare wood drink paint. Prime first, or expect coverage closer to 250–300 sq ft per gallon.
- Dark-to-light color changes almost always need two coats, sometimes three.
- Buy trim and ceiling paint separately — they use different finishes (semi-gloss for trim, flat for ceilings).
- Keep the lot number. If you have to return for more, matching the same batch avoids subtle color shifts.
Want a deeper walkthrough with room-by-room examples? Read our guide on how much paint you need, or grab the right gear with our essential painting tools list.
Paint costs in 2026
What you'll spend depends mostly on DIY vs. hiring out and the paint tier you choose. Here's where the money goes:
| Cost item | What it covers |
|---|---|
| Wall paint | ~2 gallons for a standard room, 2 coats |
| Primer | New drywall, bare wood, or big color changes |
| Trim & ceiling paint | Bought separately — different finishes |
| Supplies / tools | Roller, brush, tray, tape, drop cloth (one-time) |
| Pro labor (if hiring) | Usually the largest part of a painter's quote |
Paint and labor prices vary by brand and region — these are planning factors, not a quote.
Common mistakes to avoid
- Skipping primer on new drywall or patches, which kills coverage and shows through.
- Not measuring first — you end up over-buying or running short mid-wall.
- Forgetting that trim and ceilings use different paint, bought separately.
- Trying to cover dark-to-light in a single coat; plan for two.
- Skimping on tape and prep, then losing the time back on touch-ups.