Paint Calculator — How Much Paint Do I Need?
Stop guessing at the paint store. Enter your room below and get an exact estimate in gallons and liters, rounded up to what you can actually buy — plus a cost estimate. Free, instant, no signup.
Quick answer
A standard 12×12 ft room with 8 ft ceilings needs about 2 gallons for two coats. Measure wall area (2 × (length + width) × height), subtract 21 sq ft per door and 15 sq ft per window, divide by your paint’s coverage (350–400 sq ft/gal), add 10% waste, and round up to the nearest quart.
10% is a safe default — covers spills, roller absorption, and future touch-ups.
Your paint estimate
Buy this much
2 gals
1.95 gal · 7.4 L exact
- Wall area
- 384 sq ft
- Minus doors & windows
- −51 sq ft
- Paintable area × 2 coats
- 666 sq ft
- With 10% waste
- 733 sq ft
Rounded up to the nearest quart — paint is sold in gallons and quarts, so you never come up short mid-wall.
How the calculation works
Professional painters don't guess — they measure. Here is the exact method this calculator uses, so you can trust (and double-check) every number:
- Wall area: for a rectangular room, that's 2 × (length + width) × ceiling height. A 12 × 12 ft room with 8 ft ceilings = 384 sq ft.
- Subtract openings: 21 sq ft per standard door, 15 sq ft per average window. You don't paint those.
- Multiply by coats: two coats doubles the area you need to cover.
- Divide by coverage: your paint can lists coverage per gallon — typically 350–400 sq ft for interior paint.
- Add waste: 10% covers roller absorption, touch-ups, and small spills.
- Round up: paint is sold in gallons and quarts, so we round up to the nearest quart. Running out mid-wall costs more than a little leftover.
Paint coverage by finish
Not all paint covers equally. Flatter finishes spread further; glossier finishes go on thicker:
| Finish | Typical coverage | Best for |
|---|---|---|
| Flat / Matte | ~400 sq ft/gal | Ceilings, low-traffic bedrooms |
| Eggshell | ~375 sq ft/gal | Living rooms, dining rooms |
| Satin | ~350 sq ft/gal | Kitchens, bathrooms, trim |
| Semi-gloss | ~350 sq ft/gal | Trim, doors, cabinets |
If your can lists an exact number, enter it in the "exact coverage" field above for the most accurate result.
Tips from the pros
- Don't forget the ceiling — measure length × width and add it as extra area (use cheap flat ceiling paint).
- Prime first on bare drywall or dramatic color changes — primer follows the same math.
- Textured walls drink paint. Bump waste to 15% for heavy texture or stucco.
- Buy it all at once. Paint mixed in different batches can vary slightly in color — one purchase = one batch.
- Save leftovers properly. Seal the can, store it indoors (not the freezing garage), and label it with the room and date.
Common questions
Want the full walkthrough? Read how to calculate how much paint you need on the HomeMeasure Pro blog.