Paint Calculator
Calculate exactly how many gallons of paint you need for any room or surface. Accounts for doors, windows, number of coats, and paint coverage per gallon.
Why coverage estimates vary
This calculator assumes one gallon covers about 350 square feet per coat, a standard industry estimate — but actual coverage varies by paint brand, wall texture, and paint color. Rough or textured walls absorb more paint than smooth drywall, and darker colors sometimes require an extra coat for even coverage.
Primer is a separate consideration — if you're painting over a drastically different color, unpainted drywall, or a stain, a dedicated primer coat is often needed before your topcoats, which isn't included in this calculation.
Rounding up on paint purchases
Since paint doesn't come in arbitrary fractional amounts, it's practical to round up to the next full gallon or quart rather than buying the exact calculated amount — leftover paint is also useful for future touch-ups, since wall paint can be hard to color-match perfectly later.
For rooms with multiple wall colors or an accent wall, calculate each section separately for the most accurate estimate rather than averaging across the whole room.
Frequently asked questions
Does this include ceiling paint?
No — this calculator estimates wall paint only. Ceilings are typically calculated separately since they often use a different paint type (flat/ceiling-specific paint) and are measured by floor area rather than wall area.
Do I need to paint 2 coats?
Two coats is standard for most projects, especially when changing colors significantly, and generally produces more even, durable coverage than a single coat — though covering a similar existing color with a fresh coat may only require one.
How much paint do I need for a 12x12 room?
A 12x12 room with 8-foot ceilings has approximately 320 square feet of wall area (minus doors and windows, typically around 250-280 paintable square feet). One gallon covers roughly 350-400 sq ft, so you typically need 1 gallon for one coat, or 2 gallons for two coats.
How many square feet does a gallon of paint cover?
One gallon of interior paint typically covers 350-400 square feet with one coat on a smooth, primed surface. Rough or porous surfaces may require more paint. Always factor in two coats for best coverage — most professional painters recommend two coats for new paint or color changes.
How do I calculate how much paint I need?
Measure the perimeter of the room, multiply by ceiling height to get total wall area. Subtract 21 sq ft per door and 15 sq ft per window. Divide by the coverage rate of your paint (usually 350-400 sq ft/gallon). Multiply by the number of coats. Add 10% waste allowance.