Enter your room's length, width, and height to find out exactly how much paint you need. Subtract area for doors and windows, choose your number of coats, and the Paint Calculator returns the total gallons of paint required along with a breakdown of wall area vs. deductions — so you buy just the right amount.
Gallons of Paint Needed
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Paint Cans (1-Gallon)
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Total Paintable Area
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Gross Wall Area
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Ceiling Area
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Deducted (Doors & Windows)
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Most interior paints cover approximately 350 to 400 square feet per gallon. Primer typically covers less — around 200 to 300 square feet per gallon. Always check the coverage stated on your specific paint can label for the most accurate estimate.
Two coats are standard for most painting projects and deliver the best color depth and durability. One coat may be sufficient when repainting a wall with a very similar color. Three coats are sometimes needed when covering a dark color with a light one, or when using a primer-paint combo.
The calculator gives you the option to include or exclude the ceiling. Ceilings are often painted a different color than walls, so many painters calculate them separately. If you are using the same paint, toggle 'Include Ceiling' to yes and the ceiling area will be added to your total.
Doors and windows are solid or glazed surfaces that you don't paint with wall paint, so their area is subtracted from the gross wall area. A standard door is approximately 20 square feet and a standard window is approximately 15 square feet.
For L-shaped or oddly shaped rooms, split the room into rectangles, calculate each section separately, then add the totals together. Enter the combined total paintable area into the calculator's coverage rate to find gallons needed.
A standard 12×14 room with 9-foot ceilings has roughly 468 square feet of gross wall area. After deducting for a door and two windows (about 50 sq ft), you have around 418 sq ft. At 350 sq ft/gallon and 2 coats, you would need approximately 2.4 gallons — so buying 3 one-gallon cans is recommended.
Yes, it is generally a good idea to round up to the next full gallon. Extra paint is useful for touch-ups, covering missed spots, and future repairs. Most retailers also allow you to return unopened cans, so there is little risk in buying one extra gallon.
Yes, exterior paints often have slightly different coverage rates due to their thicker formulation and the texture of exterior surfaces. Rough or porous surfaces like brick or stucco absorb more paint and will require more gallons than smooth drywall. Always consult the coverage rate on the specific product label.