Paint Square Footage Calculator

Buy too little paint and you're back at the store mid-project, hunting for the same batch number. Buy too much and you've got half-full cans hardening in the garage. The fix is simple math: figure out the square footage you're painting, divide by how far a gallon goes, and multiply by the number of coats. Enter your wall dimensions below and the calculator handles the rest.

How to calculate paint square footage

Painting square footage is wall area, not floor area. You measure the walls, subtract the openings you won't paint, and account for coats.

Here's the whole process:

Find the perimeter of the room. Add up the length of every wall along the floor. For a rectangular room, that's 2 x (length + width).
Multiply perimeter by wall height. Most rooms have 8 foot ceilings, so a room with a 52 foot perimeter gives you 52 x 8 = 416 square feet of wall.
Subtract the doors and windows. A standard interior door is about 21 square feet (roughly 3 feet by 7 feet). A typical window runs around 15 square feet, though yours may differ, so measure the big ones. Skip subtracting for small windows if you want a little cushion.
Multiply by the number of coats. Two coats is standard for a color that covers well. Going from a dark wall to a light one, or painting bare drywall, can push you to three.
Divide by coverage per gallon. A gallon of interior latex usually covers 350 to 400 square feet on a smooth, previously painted wall. Sherwin-Williams and most manufacturers print a coverage range right on the can, so check yours before you commit.

If you're painting the ceiling too, that's just the floor area (length x width) added on top, since a flat ceiling matches the footprint of the room.

Coverage isn't a fixed number

The 350 to 400 range assumes a smooth surface and a decent paint. Real coverage drops when the surface soaks up product. Fresh drywall, patched spots, rough stucco, and textured walls all drink more paint. Cheap flat paint also spreads thinner than a premium self-priming line. When in doubt, plan for the low end of the range and you'll rarely come up short.

Coverage by surface type

Coverage per gallon shifts with what you're painting. Treat these as planning numbers per coat, and always check the range on your can.

Surface	Approx. coverage per gallon (per coat)	Notes
Smooth, previously painted drywall	375 to 400 sq ft	Best case; the number on most cans
New or bare drywall	250 to 350 sq ft	Prime it first, then the topcoat behaves normally
Light texture (orange peel, knockdown)	300 to 350 sq ft	The raised profile adds surface area
Heavy texture (popcorn, sand, stucco)	200 to 275 sq ft	All the nooks soak up product
Primer	200 to 350 sq ft	Varies a lot by brand and surface
Exterior siding (smooth)	300 to 400 sq ft	Roughly the same as smooth interior
Rough exterior (stucco, split-face block, rough wood)	150 to 250 sq ft	Can be half of the smooth number

The rougher and thirstier the surface, the fewer square feet you get. A textured accent wall or a stucco exterior can cut coverage nearly in half, so estimate those separately.

Worked example: a 12 by 14 room

Say you're repainting a 12 foot by 14 foot bedroom with 8 foot walls, one door, two windows.

Perimeter: 2 x (12 + 14) = 52 feet
Gross wall area: 52 x 8 = 416 square feet
Openings: one door (21) plus two windows (30) = 51 square feet
Net wall area: 416 - 51 = 365 square feet
Two coats: 365 x 2 = 730 square feet of coverage
Gallons: 730 / 375 = 1.95, round up to 2 gallons

Two gallons covers the walls with a little to spare. The ceiling is 12 x 14 = 168 square feet, and two coats (336) fits inside one gallon of ceiling paint. So the full job is roughly 2 gallons of wall color plus 1 for the ceiling. That tracks with what people report in practice: in a Quora thread on covering a 500 square foot room in two coats, the answers land around two to three gallons once you count the second coat and touch-ups.

Handling two coats and a color change

A coat is a full pass over the whole surface, not a touch-up, and that's where estimates go wrong. Two coats is the default: the first lays down the color, the second evens out sheen and hides roller lines. Budget for two unless you're refreshing the exact same color over a clean, sound wall.

A color change adds coats on top of that:

Similar shades, light to light or same family. Two coats usually does it.
Light over dark (white over a navy or charcoal). Plan on three coats of finish paint, or two coats over a tinted primer, which is the smarter route. Gray-tinted primer knocks down a dark base far faster than more white.
Strong colors (true red, bright yellow, deep orange). These pigments are translucent and often need three coats even over primer. Buy extra up front.

Priming for the hard cases beats burying the old color under coat after coat of expensive finish paint. One coat of primer plus two of color almost always beats four coats of color, and costs less.

Ceiling and trim are separate calculations

Walls, ceilings, and trim use different products, so estimate each on its own line.

Ceiling. A flat ceiling equals the floor area, length times width. For the 12 by 14 room, that's 168 square feet. Ceiling paint covers a touch less than wall paint because it's thick and drip-resistant, so figure 300 to 350 square feet per gallon. Two coats over 168 square feet is 336 square feet, still inside one gallon.

Trim. Baseboards, casings, and window frames don't measure cleanly in square feet, so estimate by linear feet and lean on how little area trim really is. A quart of trim enamel covers the baseboards and casings of an average room; a gallon handles several rooms. Buy by the quart for one or two rooms and step up only for a bigger job, since trim enamel is pricey and a little goes far.

Worked example: a 12 by 12 room with the openings subtracted

Take a square 12 by 12 room with 8 foot ceilings, one door, and two windows. This is one of the most searched room sizes, so here's the full walk-through.

Perimeter: 2 x (12 + 12) = 48 feet
Gross wall area: 48 x 8 = 384 square feet
Openings: one door (21) plus two windows (15 each, so 30) = 51 square feet
Net wall area: 384 - 51 = 333 square feet
Two coats: 333 x 2 = 666 square feet of coverage needed
Gallons: 666 / 375 = 1.78, round up to 2 gallons

So a 12 by 12 room takes 2 gallons for the walls in two coats, with enough left for touch-ups. Add roughly 1 gallon of ceiling paint (144 square feet, two coats is 288) and a quart of trim enamel, and you've priced the whole room. That two-gallon wall figure matches the common guidance from paint estimators for a standard 12 by 12 with 8 foot walls.

Don't forget primer

Primer is separate paint, and it counts. You need it for bare drywall, stains or water marks, or a big color jump. Coverage is similar to paint, often 200 to 400 square feet per gallon, so estimate it the same way you estimate a coat of color. It earns its keep on bare or patched drywall (paper and joint compound absorb at different rates, so an unprimed wall dries blotchy), on dark-to-light changes (tinted gray primer beats three or four coats of white), and on glossy surfaces that need something for the topcoat to grip.

Paint-and-primer-in-one products are fine over an existing painted wall in good shape. They are not a real substitute for dedicated primer on bare or problem surfaces, whatever the label promises.

Leftover paint and touch-ups

Rounding up means you'll finish with paint in the can, and that's a feature. Keep a labeled quart of every color, since dings and scuffs are a matter of when, not if. Write the room, the color name, the sheen, and the store's paint code on the lid with a marker, because that code is what lets the store re-tint an exact match years later.

A sealed can of latex stored somewhere that never freezes stays usable for a couple of years. Freezing ruins it, so keep it out of an unheated garage through winter. When you touch up, feather the paint out from the center of the spot and blend the edges; a dead-square patch will flash even in a perfect color match. Have most of a gallon left with no use for it? Most areas run paint recycling or hazardous-waste drop-offs, which beats letting it harden.

Common mistakes when estimating paint

Measuring floor area instead of wall area. A 12 by 14 room is 168 square feet of floor but 416 of wall. Paint the walls, so measure the walls.

Forgetting the second coat. One coat rarely looks finished. Double your coverage number unless it's a light refresh in the same color.

Trusting the high end of coverage. "Up to 400 square feet" is a best case on smooth, sealed walls. Budget closer to 350 on anything textured or thirsty.

Ignoring the ceiling and trim. These are separate quantities in separate products. Estimate each one on its own.

Rounding down on gallons. Round up. Running out with one wall left is worse than a spare quart.

For a deeper walkthrough of measuring any space, the how to calculate square footage guide covers odd shapes and mixed rooms. If you're only after the raw wall numbers, the wall square footage calculator breaks down a single wall or a whole room. To size the room itself, use the room calculator or start from the homepage.

Frequently asked questions

How much paint do I need for a room?

Measure the wall perimeter, multiply by ceiling height, subtract doors and windows, then multiply by two for two coats. Divide that by 375 square feet per gallon. A typical 12 by 14 bedroom with 8 foot walls needs about 2 gallons for the walls and 1 gallon for the ceiling.

How many square feet does a gallon of paint cover?

Most interior latex paints cover 350 to 400 square feet per gallon on a smooth, previously painted surface. Rough, textured, or bare surfaces cover less because they absorb more. Check the coverage range printed on the can, and plan for the lower end to be safe.

How do I calculate square feet for painting?

Multiply the room perimeter by the wall height to get gross wall area, then subtract about 21 square feet per door and 15 square feet per window. That net figure is your paintable square footage. Multiply by the number of coats before converting to gallons.

Do I count doors and windows in paint square footage?

Subtract the large ones. A standard door is roughly 21 square feet and a typical window about 15, so removing them keeps your estimate from running high. Small windows can be left in as a built-in cushion. If a wall is mostly glass, definitely subtract it.

How many coats of paint do I need?

Two coats is standard and gives even color and durability. You can sometimes get away with one when refreshing the same color over a clean wall. Plan on three coats for dark-to-light changes, bright colors like red and yellow, or bare drywall even after priming.

How much paint for a 12x12 room?

A 12 by 12 room with 8 foot ceilings has 384 square feet of wall. Subtract about 51 square feet for a door and two windows, and two coats needs roughly 666 square feet of coverage, which is 2 gallons of wall paint. Add about a gallon for the ceiling and a quart for the trim if you're doing those too.

How much does it cost to paint a room?

For a DIY room, two gallons of decent interior latex runs about $70 to $140, ceiling paint adds $30 to $50, and rollers, brushes, tape, and drop cloths another $30 to $60. That's roughly $120 to $250 in materials depending on paint quality. A hired painter charges more in labor than materials, so accurate measuring and doing it yourself saves the most on small rooms.

How much paint do I need for a textured or accent wall?

Textured surfaces cut coverage, so estimate them separately. Light texture like orange peel drops a gallon to around 300 to 350 square feet; heavy texture like popcorn or stucco can fall to 200 to 275. Measure the textured wall on its own, use the lower number, and still plan for two coats.

Can I use wall paint on the ceiling and trim?

You can, but the right product for each gives better results. Ceiling paint is thick and flat to hide imperfections and resist drips, while trim enamel dries harder and glossier to take scuffs and cleaning. Flat wall paint on trim marks up easily, so a quart of proper enamel is worth it.