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How Many Gallons of Paint Do You Need for One Room?

Last updated: May 2026
Quick answer: Most standard rooms (10×10 to 12×12 ft) need 2 to 2.5 gallons for 2 coats of wall paint. Larger rooms need 3–4+ gallons. The rule of thumb: one gallon covers ~350 sq ft per coat, so multiply your wall area by coats, divide by 350, and add 10% for touch-ups.

The question sounds simple, but "how many gallons for one room" depends on four variables: the room's size, its ceiling height, the number of coats you apply, and whether you're painting the ceiling too. Get any of these wrong and you'll either run out mid-wall or waste money on paint that sits in your garage forever.

This guide gives you the formula, a complete room size chart, and an interactive calculator that does the maths for you.

🎨 Room Paint Calculator Open full calculator ↗

The formula: how to calculate paint gallons for any room

Every paint calculation uses the same four-step process. Here it is, with a worked example for a 12×12 room:

1

Calculate your wall area

Add up the perimeter of the room (length + width + length + width) and multiply by the ceiling height. This gives you total wall area in square feet.

12 + 12 + 12 + 12 = 48 ft perimeter × 8 ft ceiling = 384 sq ft
2

Subtract doors and windows

Each standard door is 3×7 = 21 sq ft. Each window averages 3×4 = 12 sq ft. Subtract these openings — you're not painting them.

384 − 21 (door) − 12 (window) = 351 sq ft paintable
3

Multiply by number of coats

Two coats is standard. Multiply your paintable area by the number of coats to get total surface area to cover.

351 sq ft × 2 coats = 702 sq ft total
4

Divide by 350, then add 10%

One gallon covers ~350 sq ft. Divide your total by 350 to get gallons needed, then multiply by 1.1 for a 10% touch-up buffer.

702 ÷ 350 = 2.0 gal × 1.10 = 2.2 gal → buy 2.5 gallons
The paint formula
Gallons needed = ( Perimeter × Height − Openings ) × Coats ÷ 350 × 1.10
Coverage assumes a smooth, previously painted surface. Add 15–20% for textured walls or bare drywall.

Gallons needed by room size — quick reference chart

All figures assume 8-foot ceilings, one door, one window, and 2 coats of paint with a 10% buffer.

Room size Typical use Paintable walls 1 coat 2 coats (recommended) 3 coats
9 × 9 ft Nursery, closet ~260 sq ft 1 gal 1.5 gal 2 gal
10 × 10 ft Small bedroom ~287 sq ft 1 gal 2 gal 2.5 gal
12 × 12 ft most common Bedroom, office ~351 sq ft 1 gal 2.5 gal 3.5 gal
12 × 14 ft Dining room ~391 sq ft 1.5 gal 2.5 gal 3.5 gal
14 × 16 ft Living room ~447 sq ft 1.5 gal 3 gal 4 gal
16 × 20 ft Large living room ~544 sq ft 2 gal 3.5 gal 5 gal
18 × 22 ft Open-plan space ~635 sq ft 2 gal 4 gal 6 gal

How ceiling height changes everything

The table above assumes 8-foot ceilings. Higher ceilings add significant wall area. Here's how it scales for a 12×12 room:

Ceiling height Wall area (12×12 room) Paint for 2 coats Buy this much
8 ft (standard) 351 sq ft 2.2 gal 2.5 gallons
9 ft 399 sq ft 2.5 gal 3 gallons
10 ft 447 sq ft 2.8 gal 3 gallons
12 ft (high ceiling) 543 sq ft 3.4 gal 4 gallons

Tips for buying exactly the right amount of paint

📏

Measure twice, buy once

Use a tape measure — don't estimate. A room that "looks like" 12×12 is often 11.5×13.5 ft. Even small differences add up to half a gallon of paint.

🧱

Account for texture

Textured walls (orange peel, skip-trowel, popcorn) absorb 15–25% more paint than smooth walls. If your walls are textured, add that buffer on top of the 10%.

🎨

Dark over light needs primer

Going from white walls to a deep colour? One coat of tinted primer dramatically reduces the number of paint coats — and saves you the cost of a third gallon.

🛒

Gallons beat quarts

Quarts cost nearly half as much as a gallon but only hold a quarter of the paint. For any room larger than a bathroom, buy full gallons — it's always cheaper per ounce.

📦

Box your cans

"Boxing" — combining all your cans into one large bucket before painting — eliminates any batch-to-batch tint variation and gives a perfectly consistent colour.

🏷️

Label your leftovers

Pour leftover paint into a smaller airtight jar and label it with the room name, colour code, and sheen. You'll need it for touch-ups 6–18 months down the road.

More paint quantity guides

→ How much paint for a 10×10 room? → How much paint for a 12×12 room? → How much paint for a bedroom? (all sizes)

Frequently asked questions

Most standard rooms (10×10 to 12×12 ft) need 2–2.5 gallons for 2 coats. Larger rooms like a 14×16 living room need 3–3.5 gallons. The exact amount depends on ceiling height, surface texture, and number of coats.
One gallon of interior wall paint covers approximately 350 square feet per coat on a smooth, previously painted surface. On bare or textured walls, expect 300 square feet or less. Matte finishes cover a little more; semi-gloss covers a little less.
Yes — for standard rooms up to about 12×12 ft with 8-foot ceilings, 2 gallons covers 2 coats with a little left over for touch-ups. For anything larger, buy 2.5–3 gallons to be safe.
Gallons are more economical for any space larger than a small bathroom or closet. A quart typically costs 50–60% the price of a gallon but holds only 25% the paint. For accent walls or touch-up jars, quarts are convenient — otherwise, buy gallons.
Yes. Light texture (orange peel) adds about 10–15% more paint consumption. Heavy texture (skip-trowel, knock-down) can add 20–30%. Factor this in before you buy, or use the calculator's output as a starting point and add the texture buffer manually.
Stop at a natural break point — a corner is ideal. Never try to blend a new batch of paint mid-wall; even the same formula can have subtle batch variations. Always buy a little more than you think you need to avoid this situation.

Calculate your exact paint needs

Enter your room dimensions and get a precise supply list — gallons, primer, roller covers, tape, and more — with links to buy everything at once.

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