Paint Calculator: How Many Gallons Do You Need?
Enter your room dimensions and we subtract doors and windows, apply your coats and coverage rate, and tell you exactly what to buy — rounded up to real can sizes.
Default 350 is the industry planning figure. Use the can's claim if you know it.
| Paintable wall area | |
| Raw gallons (with waste) | |
| Buy |
What else do you need?
Paint Cost Estimator →
Gallons × paint tier + supplies = total project cost.
How Much Paint Per Room →
Quick-reference table for common room sizes.
Do You Need Primer? →
When primer is required and when it's a waste of money.
Paint Finish Chooser →
Flat vs eggshell vs satin vs semi-gloss, room by room.
Our picks for rollers, brushes, tape, and sprayers will appear here.
Disclosure: As an affiliate, we may earn a commission if you buy through links on this page — at no extra cost to you.
Frequently asked questions
How much paint do I need for a 12×12 room?
About 2 gallons for two coats: 384 sq ft of wall minus one door and two windows leaves 333 sq ft; two coats ÷ 350 sq ft/gal ≈ 1.9 gallons, rounded up to 2.
How many square feet does a gallon cover?
Most interior paints claim 250–400 sq ft per gallon for one coat. 350 is the standard planning figure; rough or porous surfaces get less.
Should I add extra for waste?
Yes, 10%. Cutting in, roller absorption, and touch-ups eat more than you think — and a second trip for a mismatched batch costs more than the extra quart.
Do I subtract doors and windows?
Yes — this calculator does it automatically using 21 sq ft per door and 15 sq ft per window.
How much does it cost to paint a room?
A typical 12×12 bedroom runs about $130–$240 DIY: 2–3 gallons at $25–$65/gal plus ~$40 in supplies. Use the cost estimator for your numbers.