Paint Calculator
Calculate how many gallons of paint you need for any room.
Breakdown
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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This calculator estimates how many gallons of paint you need to cover a room's walls. Enter your measurements and the result updates instantly.
- Enter the room dimensions. Measure the length and width of the room in feet, then enter the ceiling height. Standard ceilings are 8 feet, but enter the actual measurement if yours differs.
- Enter the number of doors and windows. Each standard door is deducted at 21 square feet and each window at 15 square feet. If you plan to paint over doors and windows, set both to zero.
- Set the number of coats. Most paint jobs need two coats for full, even coverage. Use one coat for a touch-up or three coats when painting over a dark color.
- Enter the coverage rate. Check the paint can label for the listed coverage in square feet per gallon. Most interior paints cover between 350 and 400 square feet per gallon. The default is 350, which is a conservative estimate that accounts for texture and absorption.
The result is always rounded up to the nearest whole gallon so you do not run short. Use the Share button to send a pre-filled link to a co-worker or contractor, or Copy to grab the result for your shopping list.
About the Paint Calculator
The calculator computes the total wall area using the formula: 2 × (length + width) × height. It then subtracts the area of all doors and windows to get the paintable area. That figure is multiplied by the number of coats and divided by the coverage rate per gallon. The result is rounded up to the nearest whole gallon using the ceiling function, because you cannot buy a fraction of a gallon at most paint stores.
This is a wall-only estimate. It does not include the ceiling, trim, or baseboards. To add the ceiling, calculate its area (length × width) separately and add the gallons needed. All calculations run entirely in your browser. No data is sent anywhere.
Frequently Asked Questions
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 surface. Textured walls, rough surfaces, or very porous surfaces will reduce coverage to as little as 250 square feet per gallon. Always check the paint can label and use a conservative estimate when buying, since it is easier to return an unopened can than to make a second trip mid-project.
How many coats of paint do I need?
Two coats is standard for most interior paint jobs and provides full, even coverage. Use one coat for touch-ups or when painting the same color. Plan on three coats when switching from a very dark color to a very light one, painting over a stain, or using a low-quality paint. Some premium paints are marketed as one-coat coverage, but two coats typically still produce a better result.
Should I include doors and windows in my paint estimate?
For walls, you should subtract the area of doors and windows because you will not paint those surfaces. This calculator deducts 21 square feet for each standard interior door (approximately 3 × 7 feet) and 15 square feet for each standard window. If you are painting non-standard openings, adjust by setting doors and windows to zero and manually reducing the room dimensions instead.
Does this calculator include the ceiling?
No. This calculator covers walls only. To estimate ceiling paint, multiply the room length by the room width to get the ceiling area in square feet, then divide by your paint's coverage rate and multiply by the number of coats. Ceiling paint typically has a higher coverage rate than wall paint because ceilings are smooth and non-porous. Most ceiling paints cover 400 square feet per gallon.