Paint calculator
Enter the room's dimensions (or total wall length) and ceiling height, choose your number of coats, and this calculator estimates the gallons of paint you need. It subtracts a standard allowance for doors and windows and assumes about 350 square feet of coverage per gallon. Add the ceiling if you're painting it too.
Based on ~350 sq ft per gallon, with doors and windows subtracted. Buy the rounded-up amount so you have enough for touch-ups — and add a primer coat for bare drywall or big color changes.
Estimates only — round up when you order, and confirm exact quantities and conversions with your supplier.
- ›1 gallon covers ≈ 350 sq ft (one coat, smooth primed wall)
- ›Door ≈ 20 sq ft · window ≈ 15 sq ft (subtracted automatically)
- ›Plan on two coats for even color and durability
- ›Add a primer coat for bare drywall, patches or big color changes
Rather not paint it yourself? Get quotes from local painters — most price by the room or by square foot.
Paint calculator — frequently asked questions
How much paint do I need?
Measure the total wall length (the perimeter of the room) and multiply by the ceiling height to get wall area in square feet, then subtract about 20 sq ft per door and 15 sq ft per window. Divide by 350 (square feet per gallon) and multiply by your number of coats. A typical 12×12 ft room needs about 1.5 gallons for two coats.
How many square feet does a gallon of paint cover?
A gallon of interior paint covers roughly 350–400 square feet in one coat on smooth, primed walls. Rough, porous or dark-over-light surfaces cover less and may need an extra coat or a primer coat. This calculator uses 350 sq ft/gallon to stay on the safe side.
Do I need one coat or two?
Plan on two coats for most jobs — it gives even color and better durability, especially over a different color, patched drywall, or when going lighter. One coat can work when you're repainting the same color over a clean, primed wall. The calculator lets you choose.
How much does it cost to paint a room?
Professionally, a single room runs roughly $300–$800 depending on size, prep and ceilings; a whole home is about $2,000–$8,000. DIY, you're mostly paying for paint at around $30–$60 a gallon. See the full interior painting cost guide for details.
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This calculator gives estimates for planning only. Round up when you order, and confirm exact quantities, coverage and weight conversions with your supplier — materials vary.