Paint Calculator
Tell us your room size and we'll estimate how much wall paint to buy — no more guessing at the store.
📖 How it works & FAQHow much paint do you actually need?
Buying paint is a guessing game if you eyeball it — grab too little and you're back at the store mid-project, grab too much and half a can dries out in the garage. This calculator works out the wall area of your room, subtracts the parts you don't paint (doors and windows), and turns that into gallons based on how many coats you're planning.
The math is simple and transparent. We take your room perimeter — that's 2 × (length + width) — and multiply by the wall height to get the total wall surface. Then we remove 21 square feet for every door and 15 square feet for every window, since you don't paint those. The leftover area is divided by 350 (the square feet one gallon typically covers) and multiplied by your number of coats.
Why two coats is usually the honest answer
One coat almost never looks finished, especially over a color change or a patchy primer. Most interior wall paints are rated for around 350 square feet per gallon per coat, so two coats effectively halves your coverage. If you're painting a light color over an existing similar shade, you might get away with one — but for anything bold, dark, or over bare drywall, plan for two and add primer.
How to use it
- Enter your room's length and width in feet, then the wall height (8 ft is standard).
- Count the doors and windows on the walls you're painting and type those in.
- Choose how many coats you want — two is the safe default.
- Read the results: gallons needed, whole cans to buy, and the wall area behind the numbers. The room preview updates as you type.
FAQ
- Does this include the ceiling?
- No — this estimates wall paint only. Ceilings use a different area (length × width) and often a separate flat ceiling paint.
- What coverage number do you use?
- 350 square feet per gallon per coat, a common average for interior latex. Check your can's label; thicker or textured walls may cover less.
- Should I round up when buying?
- Yes. The "1-gallon cans" figure already rounds up, and a little extra is handy for touch-ups later.
- Are these numbers exact?
- These are estimates, not professional advice — surface texture, color changes, and application method all affect real usage.