Paint Pals · Paint Calculator
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Paint calculator: how much paint do I need?

Enter a room size (or the wall square footage if you already have it), pick your coats, and get the exact gallons to buy — doors and windows deducted, coverage adjustable, the round-up explained. No made-up numbers.

How do you want to enter the room?

We subtract 21 sq ft per door and 15 sq ft per window — you don't paint the glass or the slab.

Coats
Paint to buy
2 gal

1.3 gal of paint needed, rounded up to whole cans.

Walls · 333 sq ft1.3 → buy 2

Buy whole gallons and get them mixed in one batch so the color matches wall to wall. Two coats isn't double the paint — the second coat goes on a sealed surface, so it uses less.

Want the full price, not just gallons? →Estimate like a pro with Paint Pals — $10/mo

How to figure out how much paint you need

Paint is sold by the gallon, so the whole job is one question: how many gallons cover your walls? Start with wall area — the room's perimeter times the ceiling height. A 12×12 room with 8-foot walls is 2 × (12 + 12) × 8 = 384 square feet. Subtract the openings you won't be rolling — about 21 square feet per door and 15 per window — and divide by the paint's coverage (usually 350–400 square feet per gallon). That's one coat; add the second and you're done.

The one thing most calculators get wrong is coats. A second coat goes on a sealed surface and uses less paint than the first — so two coats is about 1.6× the paint, not double. This tool uses the real per-coat amounts from a working painting company's standards, then rounds up to whole gallons because that's how you buy it.

Coverage: read the can, then adjust

"350–400 square feet per gallon" assumes a smooth, previously painted wall. Reality changes it: fresh drywall and porous surfaces soak up more, deep and vivid colors often need an extra coat to look even, and textured or rough walls have more actual surface than their footprint suggests. If any of that's you, lower the coverage number in the calculator and it recomputes. Buy your gallons mixed in a single batch so the color is identical wall to wall — two cans of the same color mixed at different times can differ just enough to see.

Where these numbers come from

The coverage and per-coat amounts here are the same ones behind our full painting estimate calculator — measured inside a real painting company and refined over years of jobs. This page just answers the narrow question "how much paint," so it's quick. When you need the whole bid — labor hours, materials, and a price to charge — the estimate calculator runs the full method, and Paint Pals turns it into options, a signed contract, and a deposit — $10/mo founding price, 30-day money-back guarantee.

Painting the outside instead? The exterior painting cost calculator handles siding, soffits, and trim with the same real math.

Paint calculator FAQ

How much paint do I need for a 12×12 room?+

A 12×12 room with 8-foot walls has about 384 square feet of wall. Take out a door and a couple of windows and you're near 333 square feet — roughly one gallon for one coat, and about 1.4 gallons for two coats, so you'd buy 2 gallons. Add the ceiling and you're at 3. The calculator above does this for your exact room, coats, and paint.

How many square feet does a gallon of paint cover?+

Most interior latex paints cover 350–400 square feet per gallon on a smooth, previously painted surface — the calculator defaults to 400, which matches common premium paints. Fresh drywall, deep colors, and rough or textured walls drink more, so drop the coverage number if that's your situation. The exact figure is on the can.

How much paint do I need for two coats?+

Not double. The first coat soaks into the surface; the second goes on a sealed wall and uses noticeably less — so two coats is about 1.6× the paint of one, not 2×. This calculator prices coats the way paint actually behaves, which is why two coats rarely doubles the gallons.

Should I subtract doors and windows?+

Yes — you don't paint the glass or the door slab with wall paint. The rule of thumb this calculator uses is about 21 square feet per door and 15 per window. On a small room those openings can be a whole gallon's difference, so the counts matter.

How much paint do I need for a ceiling?+

Turn on "Also painting the ceiling?" and the calculator adds it. A ceiling is length × width, and flat ceiling paint typically needs a bit more per square foot than walls, so a 12×12 ceiling is usually one gallon. It's kept as its own line because ceiling paint is a different product from your wall color.

Does this include primer?+

No — this counts finish paint only. Bare drywall, big color changes, and stain-blocking situations need primer, which is a separate product bought roughly like a coat of paint. If you're changing color dramatically or painting new drywall, plan on primer plus your two finish coats.

Just want the price, not the gallons?+

This tool answers "how much paint," not "what should I charge." For a full contractor-grade estimate — labor hours from real production rates, materials, and a price — use the painting estimate calculator. It's the same math a real painting company runs on.

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