How Much Paint Do I Need?

Enter your room dimensions to find out exactly how many gallons of paint to buy — walls, ceiling, and trim calculated separately.

Looking for price, not quantity? A gallon of interior paint costs $20–$80 in 2026 depending on brand and quality tier — see the full price guide by brand or the total project cost calculator. This tool below calculates how many gallons you need.

How to Calculate Paint for a Room

To calculate paint needed, find the total wall area by multiplying room perimeter by ceiling height. Subtract 21 sq ft per door and 15 sq ft per window. Divide by 350 (sq ft per gallon) and multiply by your number of coats.

For a standard 12×10 room with 8-ft ceilings, 1 door, and 2 windows, you'll typically need about 1.5 gallons for two coats of wall paint.

How Many Coats of Paint Do I Need?

Most paint jobs require 2 coats for an even finish. One coat is only sufficient when repainting with the same or similar color. Going from dark to light always requires at least 2 coats, sometimes 3.

Paint Coverage Quick Reference

Room Size	Approx Wall Area	Gallons (2 coats)
10×10 ft, 8 ft ceiling	~290 sq ft	2 gallons
12×12 ft, 8 ft ceiling	~330 sq ft	2 gallons
14×16 ft, 8 ft ceiling	~400 sq ft	3 gallons
16×20 ft, 8 ft ceiling	~490 sq ft	3 gallons

Coverage rates assume 350 sq ft per gallon per coat, which is a conservative industry standard. Higher-quality paints may cover up to 400 sq ft per gallon. Dark colors applied over light walls may need a third coat — especially deep blues, reds, and blacks.

Paint Finish Guide: Which Sheen for Which Room?

Paint sheen affects both appearance and durability. Flat and matte finishes hide surface imperfections well but don't clean easily; high-gloss finishes are the most durable and washable but show every surface flaw. Choosing the wrong finish for a high-traffic area is a common mistake.

Finish	Sheen Level	Best For	Washability
Flat / Matte	None	Ceilings, low-traffic walls	Poor — marks easily
Eggshell	Low	Living rooms, bedrooms	Moderate
Satin	Medium	Kitchens, bathrooms, hallways	Good
Semi-gloss	High	Trim, doors, cabinets	Very good
Gloss	Very high	Furniture, exterior trim	Excellent

For most rooms, eggshell or satin on walls with semi-gloss on trim and doors is the standard approach. Bathrooms and kitchens benefit from satin or semi-gloss on walls due to moisture and the need to wipe surfaces clean.

Common Paint Buying Mistakes

• Rounding down instead of up. If the math says 1.6 gallons, buy 2 — not 1 plus a quart "just in case." Running out mid-wall means a store trip and a visible seam where old and new batches meet.
• Budgeting the same for every color change. A dramatic shift (white to navy, tan to black) can eat a third coat even with primer. Add a half-gallon buffer for dark or saturated colors going over light existing walls.
• Forgetting trim and doors need a separate can. Wall paint quantity doesn't cover trim, baseboards, or doors — those use a different (usually semi-gloss) product, bought and calculated separately.
• Mixing cans from different batches without boxing them. Two gallons of the "same" color from different production lots can show a subtle tone difference on the wall. Buy all cans in one trip, or ask the store to box (combine) them in one bucket first.
• Assuming paint-and-primer-in-one halves your coat count. It still needs the same number of coats as separate primer + paint on porous or dark surfaces — it's a convenience product, not a shortcut.

Frequently Asked Questions

How many gallons of paint do I need for a 12x12 room?

A 12x12 room with 8-ft ceilings has about 320 sq ft of wall area, roughly 270 sq ft net after subtracting doors and windows. One gallon covers about 350 sq ft per coat, so one coat needs about 1 gallon; plan on 2 gallons for two coats.

Do I need to paint the ceiling separately?

Yes. Ceilings usually use flat ceiling paint, not wall paint, and are calculated by floor area (length x width) rather than perimeter, since a ceiling has no doors or windows to subtract.

How much paint should I buy for two coats?

Multiply your one-coat gallon estimate by roughly 1.8-2, since the first coat seals the surface and the second coat typically covers slightly more efficiently.

Does paint sheen affect how much I need?

No. Sheen (flat, eggshell, satin, semi-gloss) doesn't change coverage rate — all standard interior paints cover roughly 350-400 sq ft per gallon per coat. Sheen affects durability and cleanability, not quantity.