How Much Paint Do I Need?

The amount of paint depends on your wall area, number of coats, and paint type. Most rooms need 2 gallons for 2 coats — but your exact dimensions change everything.

The quick formula

Gallons = (Wall area − openings) × coats × (1 + waste) ÷ coverage (sq ft/gal)

Step-by-step: how to measure

Measure each wall — length × ceiling height in feet
Add all walls together — total gross wall area
Subtract openings — standard door: 21 sq ft · standard window: 15 sq ft
Multiply by coats — usually 2 for full coverage
Divide by coverage — 350 sq ft/gallon for standard paint

Paint coverage by type

Paint type	Coverage per gallon
Standard interior	350 sq ft
Premium / self-priming	400 sq ft
Primer	250 sq ft
Textured / rough walls	275 sq ft

Gallons needed by room size (2 coats, standard paint, 8 ft ceiling)

Room size	Wall area	Net area*	Gallons
8 × 10 ft	288 sq ft	237 sq ft	2
10 × 12 ft	352 sq ft	301 sq ft	2
12 × 12 ft	384 sq ft	333 sq ft	2–3
12 × 16 ft	448 sq ft	397 sq ft	3
14 × 20 ft	544 sq ft	493 sq ft	3

After subtracting 1 door (21 sq ft) and 2 windows (30 sq ft). Rounded up to nearest gallon.

Tips to avoid buying too much or too little

Buy a test quart for new colors before committing to gallons
Keep a leftover quart for touch-ups — store it upside-down to create an airtight seal
Don’t forget the ceiling — if painting the ceiling, add length × width to your total
Trim and doors paint separately — use a different can/color for trim

Use the Paint Calculator for your exact room dimensions, openings, and number of coats.

Frequently Asked Questions

How many gallons of paint for a 12×12 room?

A 12×12 room with 8-foot ceilings has about 384 sq ft of wall area. After subtracting 1 door and 2 windows (~51 sq ft), net area is 333 sq ft. At 2 coats and 350 sq ft/gallon, you need about 2 gallons. Always round up — buy 3 gallons.

How much paint do I need for a bedroom?

An average US bedroom (10×12 ft, 8 ft ceiling) has about 352 sq ft of walls. After 1 door and 2 windows, net area is roughly 301 sq ft. Two coats at 350 sq ft/gallon = about 2 gallons. Most bedrooms take 2–3 gallons for 2 coats.

How many coats of paint do I need?

Two coats is standard for most painting projects. If painting a dark color over light (or vice versa), a third coat may be needed. Priming first reduces the coats required for dramatic color changes.

How much does a gallon of paint cover?

Most standard interior paints cover 350–400 sq ft per gallon per coat on smooth surfaces. Textured or porous surfaces absorb more paint and may only yield 250–300 sq ft per gallon.

Should I buy a quart or a gallon of paint?

A quart covers about 87–100 sq ft per coat. For small accent walls or touch-up projects under 100 sq ft, a quart may be enough. For full rooms, gallons are more economical.