NumberTally Paint Calculator
How much paint do you actually need? Enter your room or wall dimensions, subtract doors and windows, pick your coats — and get the paintable area, gallons to buy (rounded up), and a primer call.
Advanced options
How much paint per square foot?
A gallon of interior paint covers about 350 square feet per coat on smooth walls — that’s the industry standard this calculator uses. Rough or textured surfaces drink more (plan on 250–300 ft²/gal), and cheap paint often needs a third coat, which wipes out any savings. Always buy whole gallons and round up: an opened gallon keeps for years, but a mid-wall color mismatch from a second batch does not.
When do you need primer?
Primer is non-negotiable on new drywall, bare wood, and drastic color changes (dark to light especially) — it seals the surface so the topcoat covers in two coats instead of three or four. For a simple repaint in a similar color, a quality paint-and-primer-in-one skips the separate step. Budget roughly the same gallons of primer as paint when it’s needed.
Frequently Asked Questions
How many square feet does a gallon of paint cover?
About 350 ft² per coat on smooth interior walls. Textured walls, brick, or rough siding drop that to 250–300 ft² per gallon.
Do I subtract doors and windows from the wall area?
Yes — a standard interior door is about 21 ft² (3×7 ft) and a typical window about 15 ft² (3×5 ft). This calculator subtracts them automatically from your counts.
Is one coat of paint enough?
Rarely. One coat leaves thin spots and uneven sheen; two coats is the professional standard for full, even coverage. Budget for two unless you’re just refreshing the exact same color.
How much paint do I need for a 12×12 bedroom?
Four 12×8 walls = 384 ft², minus a door (21) and two windows (30) = 333 ft². At 350 ft²/gal that’s 1 gallon per coat — so 2 gallons for two coats.
Can I use the leftover paint later for touch-ups?
Yes — sealed and stored at room temperature, latex paint lasts 2–10 years. Keep the label with the color formula; touch-ups from the same can are invisible, a new batch may not match exactly.