# How Much Paint Do I Need for a Room?
I once bought six gallons of paint for a single bedroom because the guy at the paint counter "rounded up to be safe." I used two and a half. The other three and a half sat in my garage for four years until I gave them away. That mistake taught me to always do the math myself — it takes five minutes and saves real money.
The formula is simple, and once you know it, you'll never guess at the paint store again. Let's walk through it with real room sizes.
The Basic Formula
Here's everything you need to know in one line:
(Total wall square footage ÷ 350) × number of coats = gallons needed
One gallon of quality interior latex paint covers about 350 square feet per coat. That's the industry standard number printed on most cans, and in my experience it's accurate for normal walls with a roller. Rough or heavily textured walls can drop that to 300 or even 250 square feet per gallon — I'll cover that adjustment below.
Two coats is the standard for any real paint job. So in practice, the formula most people need is:
(Wall square footage ÷ 350) × 2 = gallons
Step 1: Measure Your Walls
Measure the length of each wall and the ceiling height. Don't measure the floor — you're painting walls, not floors.
Wall area = (length of wall × ceiling height), added up for all four walls. Or faster: measure the perimeter of the room (add up all four wall lengths) and multiply by ceiling height.
Example — my spare bedroom: The room is 10 ft by 12 ft with 8-foot ceilings. Perimeter = 10 + 10 + 12 + 12 = 44 feet. Wall area = 44 × 8 = 352 square feet.
Step 2: Subtract Doors and Windows
A standard interior door is about 21 square feet (3 ft × 7 ft). A standard window is about 15 square feet (3 ft × 5 ft). You don't need exact numbers — just subtract these rough values.
My 10×12 spare bedroom has one door and two windows: 352 − 21 − 15 − 15 = 301 square feet of actual paintable wall.
If you want to be fast and conservative, skip this step entirely. Overestimating by 50 square feet just means you have a little extra for touch-ups, which you'll want anyway.
Step 3: Divide by Coverage and Multiply by Coats
301 sq ft ÷ 350 = 0.86 gallons per coat. Two coats = 1.72 gallons.
Paint comes in quarts and gallons. 1.72 gallons means you buy 2 gallons. You'll use about 1.7 and have a third of a gallon left for touch-ups — which is exactly what you want. Never return your leftover paint; a labeled leftover can saves you a store trip every time a kid scuffs the wall.
Quick Reference Table: Common Room Sizes
I built this table from rooms I've actually painted. It assumes 8-foot ceilings, one door and one window subtracted, and two coats. Round up to the nearest gallon.
| Room Size | Wall Sq Ft (approx) | Gallons for 2 Coats | What to Buy |
|---|---|---|---|
| 10×10 bedroom | 280 | 1.6 | 2 gallons |
| 10×12 bedroom | 301 | 1.7 | 2 gallons |
| 12×12 bedroom | 348 | 2.0 | 2 gallons |
| 12×15 master bedroom | 395 | 2.3 | 3 gallons |
| 14×16 bedroom | 443 | 2.5 | 3 gallons |
| 16×20 living room | 539 | 3.1 | 4 gallons (or 3 + 1 quart) |
| 20×24 great room | 665 | 3.8 | 4 gallons |
If your ceilings are 9 feet instead of 8, add roughly 12% to the gallon count. For 10-foot ceilings, add about 25%.
Worked Example: A 16×20 Living Room With a Fireplace Accent Wall
Let me show you a slightly trickier real case — my living room, which has an accent wall in a different color.
The main walls: Room is 16×20 ft, 8-ft ceilings. Perimeter = 72 ft. Wall area = 72 × 8 = 576 sq ft. Subtract two doors (42 sq ft) and three windows (45 sq ft) = 489 sq ft. But one 16-ft wall (128 sq ft) is the accent wall, painted a different color. Main color area = 489 − 128 = 361 sq ft.
361 ÷ 350 = 1.03 gallons per coat × 2 coats = 2.06 gallons → buy 2 gallons of the main color (and you'll have just enough; I'd grab a quart too if the color is custom-mixed, since matching it later is a pain).
The accent wall: 128 sq ft ÷ 350 = 0.37 per coat × 2 = 0.73 gallons → buy 1 gallon of the accent color.
Total: 3 gallons across two colors. This is why accent walls save money — that one gallon of deep color cost me $48, versus a fourth gallon of the main color I'd barely have touched.
Adjustments for Special Cases
Textured walls. Knockdown, orange peel, or popcorn texture eats paint. Use 300 sq ft per gallon for light texture, 250 for heavy texture. My hallway with heavy knockdown texture used 30% more paint than the formula predicted — I had to make a mid-project store run, which is exactly what this guide is trying to save you from.
Dark color over light (or the reverse). Going from dark to light usually needs a coat of primer plus two coats of paint — budget as if it's three coats of coverage, or buy a tinted primer (tinted toward your final color) and two gallons of paint. Going light to dark is easier; two coats usually does it.
Ceilings. Ceiling paint covers about 350 sq ft per gallon too, but ceilings almost always need just one good coat if you're using flat white ceiling paint. A 10×12 room has 120 sq ft of ceiling — one gallon handles it with plenty to spare.
Primer. Only count primer separately if you're priming. Spot-priming patches uses almost nothing — a quart is plenty. Full-room primer: use the same formula, one coat.
How Much Does the Paint Cost?
Here's what the math means for your wallet, using typical mid-grade paint prices:
| Paint Tier | Price per Gallon | 10×12 Room (2 gal) | 16×20 Room (3–4 gal) |
|---|---|---|---|
| Budget ($22/gal) | $22 | $44 | $66–$88 |
| Mid-grade ($40/gal) | $40 | $80 | $120–$160 |
| Premium ($55/gal) | $55 | $110 | $165–$220 |
Here's my honest take after painting a dozen rooms: mid-grade paint is the value sweet spot. Budget paint is thinner — I once needed three coats of a $22 paint where two coats of $40 paint would have done it. Three gallons of cheap paint ($66) cost more than two gallons of good paint ($80)? No — $66 is less than $80. But add the extra Saturday I spent on that third coat, and the cheap paint was the most expensive paint I've ever bought.
The 10% Touch-Up Rule
Whatever the formula says, I always make sure I have at least 10% extra — roughly an extra quart for a bedroom. Here's why:
- Touch-ups in the first month are inevitable (furniture scuffs, outlet cover edges, the spot you missed).
- Custom-mixed colors can vary slightly between batches. Paint from the same can always matches.
- An unopened can can be returned; an opened can usually can't, but a half-gallon of leftover wall color is worth more than the $20 refund.
Label every leftover can with the room, the color name and code, the date, and which walls. Future you will be grateful.
Common Mistakes
Buying based on floor square footage. A 10×12 room is 120 sq ft of floor but 300+ sq ft of wall. This is the single most common error, and it leaves people halfway through coat one with an empty can.
Forgetting the second coat in the math. The can says 350 sq ft per gallon — per coat. Double it. I've watched neighbors buy exactly enough for one coat and act surprised.
Not adjusting for texture. If your walls have heavy texture and you use the 350 number, you'll run short by 20–30%. Use 250–300 for textured walls.
Buying five gallons to "save money" on a bulk discount. The 5-gallon bucket is cheaper per gallon, but only if you'll use it. Three leftover gallons in the garage for five years is not savings.
Returning all the extra. Keep at least a quart of every color you put on your walls. Touch-up paint is priceless when you need it and a store trip when you don't have it.
FAQ
How many square feet does a gallon of paint cover? About 350 square feet per coat on smooth walls with a roller — that's the standard figure on most paint cans. Drop to 300 for lightly textured walls and 250 for heavy texture. These numbers assume proper application, not a thin skim coat.
How much paint do I need for a 12×12 room? A 12×12 room with 8-foot ceilings has about 348 square feet of paintable wall after subtracting a door and window. At 350 sq ft per gallon and two coats, you need exactly 2 gallons. Buy 2 gallons and you'll have a little left for touch-ups.
Is one gallon of paint enough for a bedroom? Rarely. One gallon covers one coat of a small 10×10 bedroom (280 sq ft of wall). Since you need two coats for an even finish, plan on 2 gallons for any bedroom. The only exception is repainting the same color over walls in great shape, where one careful coat can work.
How much paint do I need for the ceiling? Measure length × width of the room. A 12×15 bedroom ceiling is 180 sq ft — well under one gallon's 350 sq ft coverage. One gallon of flat ceiling paint handles any normal bedroom ceiling in one coat, with plenty left over.
Should I buy extra paint for touch-ups? Yes — keep at least a quart of each wall color, labeled with the room and color code. Custom-mixed colors can shift slightly between batches, so touch-up paint from the original can is the only guaranteed match.
About the Author
Dave Collins is a hands-on DIY enthusiast who has spent the past 15 years renovating three of his own homes. He learned most of what he knows by making mistakes first, then asking pros what he did wrong. On this site he writes practical, numbers-first guides so you can skip the mistakes and get it right the first time.