Buy too little paint and you make a second trip. Buy too much and you waste money. The good news is that the math is simple. Here is how to work out exactly how much you need.
The Quick Answer
- One gallon of paint covers about 350 to 400 square feet on a smooth wall. Check the can label for your brand.
- Most walls need two coats.
- An average bedroom (12 x 14 feet, 8-foot ceilings) needs about 2 to 3 gallons for walls.
Want it done for you? Try our paint coverage calculator. Enter your room size and it gives you the gallons.
How to Figure It Out in 4 Steps
Worked example: A 12 x 14 room has 416 square feet of wall. One door and two windows take away about 50. That leaves 366. Two coats makes 732. Divide by 350 and you get 2.1 gallons. Buy 3, or buy 2 gallons plus a quart.
Paint Needed by Room Size
This chart assumes 8-foot ceilings, one door, two windows, and two coats. Ceilings and trim are extra.
| Room size | Wall area | Gallons (walls only) |
|---|---|---|
| 10 x 10 ft | 270 sq ft | 2 |
| 12 x 12 ft | 334 sq ft | 2 |
| 12 x 14 ft | 366 sq ft | 3 (or 2 + a quart) |
| 14 x 16 ft | 430 sq ft | 3 |
| 16 x 20 ft | 526 sq ft | 4 |
Do Not Forget the Ceiling and Trim
The ceiling area is just length times width. A 12 x 14 ceiling is 168 square feet. One gallon covers it with a coat to spare. For trim and doors, a quart is usually enough for an average room.
What Changes the Number
These things make a room use more paint than the math says:
- Rough or textured walls. They soak up more paint.
- New drywall. It drinks paint. Prime it first.
- Big color changes. Going from dark to light often needs primer plus extra coats.
- Cheap paint. Thin paint covers less. You may need a third coat.
Supplies That Make the Job Easier
Good prep makes the paint go on better. You will also waste less. Here is a short list of what we would buy.
Common Mistakes to Avoid
Doing a Small Project?
Crafts and small items need far less than a gallon. For ideas, see our guide to the best paint for pumpkins.
Frequently Asked Questions
How much paint do I need for a 12 x 12 room?
About 2 gallons for the walls with two coats, assuming 8-foot ceilings, one door, and two windows. Add a bit more if the walls are rough.
How many square feet does a gallon of paint cover?
Usually 350 to 400 square feet on smooth walls. The can will list the exact number for that brand.
Do I need two coats of paint?
Most of the time, yes. Two coats give an even color and good coverage. A single coat may work if the new color is close to the old one and the paint says it has primer built in.
How much paint do I need for a ceiling?
Multiply the room length by the width. One gallon usually covers a ceiling up to about 350 square feet in one coat.
Should I buy extra paint?
Yes. Round up to the next gallon. Leftover paint is handy for touch-ups later.
Daniel Carter covers the practical side of home improvement at The Dailey House — drainage fixes, DIY yard projects, patio makeovers, and the kind of weekend builds that actually get finished. If there's a smarter or cheaper way to do it, he's tested it.