Paint Calculator
Work out how much paint a room really takes with this paint calculator. Type the room size, count the doors and windows, pick your surface and coats, and read the full buy list in one result. The tool shows the paintable area, the exact gallons, and the buy line in gallons and quarts, the cans the store sells. Primer and ceiling paint get their own lines, and a price per gallon turns the count into a cost.
What the result numbers mean
Your wall paint, rounded up to whole gallons and quarts. Paint sells in those two cans, so the buy line speaks the shelf language.
Your wall area after doors and windows come out. This is the ground the coats must cover.
The true math before the round up to cans. The gap between this line and the buy line is your safety margin.
Turn the ceiling on and its paint counts apart, one coat over the room area. Ceiling paint is often a flat white of its own.
Turn primer on and it counts at 300 square feet per gallon, one coat under the paint. New drywall and bare wood drink the top coat without it.
Add a price per gallon and the tool prices the wall paint, with quarts at 40 percent of the gallon price. Primer and ceiling paint price apart.
How much paint do I need for a 12x12 room?
A 12 by 12 foot room with 8 foot walls holds 384 square feet of wall. One door and one window take it to 348 square feet. Two coats at 350 square feet per gallon need 1.99 gallons, so buy 2 gallons.
How the math works
Type the length, the width and the wall height in feet. Measure wall to wall, and use the true ceiling height, not a guess.
Each door takes out 21 square feet and each window 15. The tool subtracts them before any paint math runs.
Area minus 21 per door, 15 per windowTwo coats is the standard plan. One coat can work over a like color. A dark color change can need three.
The surface sets coverage per gallon. Smooth drywall covers 400 square feet. Stucco covers only 175, because the rough face drinks paint.
Cover needed / Coverage per gallonPrimer counts apart at 300 square feet per gallon, one coat. The ceiling counts apart at one coat over the room area.
The buy line rounds the exact gallons up to whole gallons and quarts. A quart costs about 40 percent of a gallon, and the cost line uses that rate.
A bedroom, 12 by 12 feet with 8 foot walls
Here is the bedroom from the quick answer, on a breakdown slip, the way the tool builds it.
Read the slip top to bottom. The deductions come before the coats, because paint never lands on a door or a window. The exact line shows the true need, and the order line rounds it up to the cans on the shelf. The paint calculator above runs your own room the same way.
Surfaces and coverage, explained
Coverage is the number that moves a paint job. This paint calculator holds a rate for each common surface, because one gallon never covers the same ground twice. Tap a card to load a 12 by 12 foot room on that surface.
The best coverage in the house. A gallon covers 400 square feet in one coat on a smooth, primed wall. New drywall still wants primer first.
Key measure: 400 sq ft per gallonTap to load in the calculatorOrange peel and knockdown textures hold more paint in their ridges. A gallon covers about 350 square feet, and ceilings run at the same rate.
Key measure: 350 sq ft per gallonTap to load in the calculatorBoards, seams and grain drink paint. A gallon covers about 275 square feet outside. The surface choice in the tool carries this rate for exterior walls.
Key measure: 275 sq ft per gallonTap to load in the calculatorMortar joints and rough faces eat paint. A gallon covers about 200 square feet, and a first coat on bare brick can take more.
Key measure: 200 sq ft per gallonTap to load in the calculatorThe roughest common face. A gallon covers about 175 square feet. Plan the full rate from the start, or the last wall runs short.
Key measure: 175 sq ft per gallonTap to load in the calculatorThe ceiling counts as one coat over the room area, at the same rate as your surface. A 12 by 12 foot ceiling needs 2 quarts on a textured rate.
Key measure: one coat, room areaTap to load in the calculatorTrim, doors and cabinets
Walls are not the whole paint job. Trim and cabinets drink their own paint, and they count in their own way.
Trim math
Trim counts by its face. A 6 inch baseboard shows half a square foot per running foot. Add the face areas up and run the total through the tool as wall area. Trim paint sells by the quart, and one quart covers about 100 square feet per coat at enamel rates.
Cabinet math
Count cabinet doors and drawer fronts on both faces, plus the frames and the box sides that show. A mid size kitchen lands near 130 square feet of cabinet surface per coat. Cabinet enamel covers about 350 to 400 square feet per gallon per coat, so two coats on that kitchen take about 3 quarts of paint. A bonding primer goes under it in one coat first.
Two coats on woodwork
Cabinets and trim take two finish coats for an even sheen. Sand lightly between coats and let each coat dry fully. The round up to whole cans in the buy line covers the small faces and edges the wall math never sees.
How accurate this estimate runs
This paint estimation follows maker coverage tables, so the count lands close when the wall matches the surface you picked. Real walls swing it. A first coat on a bare or rough surface drinks more paint, and a smooth primed wall can stretch a gallon further.
Two guards keep the number honest. The tool plans at the stated rate for your surface, never at the best case on the can. Then it rounds the buy line up to whole cans. That round up is your cushion for cut ins, spills and thin spots in the second coat.
Paint numbers, in one place
| Surface | Square feet per gallon |
|---|---|
| Smooth drywall | 400 |
| Textured walls | 350 |
| Wood siding | 275 |
| Brick | 200 |
| Stucco | 175 |
Common mistakes
A dark color over a light wall, or the flip, shows through at one coat. Plan two coats, and three when the change is strong.
Openings take no paint. Leave four doors and windows in the area and you buy paint for walls that do not exist.
Bare drywall drinks the top coat and the finish dries flat and uneven. One primer coat at 300 square feet per gallon saves the paint coats.
Stucco at the drywall rate runs out near the last wall. Match the surface choice to the real wall before you buy.
How to buy paint for your job
The result moment is the buying moment. Take the buy line from this paint calculator to the paint counter. Two routes cover almost every room job.
Option A: Paint it yourself
- Buy the buy line, gallons and quarts as the tool splits them. Quarts cost about 40 percent of a gallon, so the split saves money on small needs.
- Put the primer can beside the paint can when the tool counts primer. New drywall and bare wood need it under the color.
- Brushes and rollers are the tools the job needs next. A good brush cuts the edges the roller never reaches.
- Keep the color name and the can label. A touch up years later matches only from that label.
Option B: Hire a painter
- A painter quotes labor and materials apart. Your gallon count from this page checks their material line.
- Ask which surfaces their quote counts, and if primer sits in it.
- High walls and exterior siding carry real ladder and spray work. That is where a pro earns the fee.
- Get the quote in writing, with coats named. One coat and two coats are two jobs.
For the wall area on its own, the square footage calculator owns bare area for any use. For the floor under the fresh paint, the flooring calculator counts boxes in the same style, and the tile calculator counts tile for the bath and kitchen walls.
Questions, answered
Related calculators
Ready to plan your project?
Pick a calculator and get your numbers in seconds.
Find your calculator