Paint Calculator
Free and simple, type your room size and get how many gallons of paint to buy. Doors and windows are taken off, and you choose the number of coats. No sign-up, no email.
Paint: Calculate
How to Use: 3 Easy Steps
Step 1: Measure your room: length, width, and wall height in feet.
Step 2: Count the doors and windows, and choose your coats, 2 coats is normal for a good finish.
Step 3: Press Calculate. You get the gallons to buy (whole gallons, like the shop sells).
Paint Formula: How to Calculate Gallons of Paint
Step A: Wall area = 2 × Wall Height × (Length + Width). Example for a 12 × 10 ft room with 8 ft walls: 2 × 8 × 22 = 352 sq ft.
Step B: Take off the parts you do not paint: a normal door is about 20 sq ft, a window about 15 sq ft. Example: 352 − 20 − 15 = 317 sq ft to paint.
Step C: One gallon covers about 350 sq ft for one coat. For 2 coats: 317 × 2 ÷ 350 = 1.81 gallons: so buy 2 gallons.
Ready Answers for Common Rooms (8 ft walls, 1 door, 1 window, 2 coats)
| Room | Area to Paint | Paint to Buy |
|---|---|---|
| Bathroom 8 × 5 ft | 173 sq ft | 1 gallon |
| Bedroom 10 × 10 ft | 285 sq ft | 2 gallons |
| Bedroom 12 × 12 ft | 349 sq ft | 2 gallons |
| Living room 15 × 12 ft | 397 sq ft | 3 gallons |
| Living room 20 × 15 ft | 525 sq ft | 3 gallons |
Coverage changes with the paint and the wall. Rough or dark walls drink more paint, the number on your can (350 is typical) is the one to trust.
Common Mistakes to Avoid
1. Planning only 1 coat. One coat almost never covers evenly, especially over a different colour. Two coats is the normal plan.
2. Not taking off doors and windows. A room with 2 doors and 3 windows has about 85 sq ft you will not paint, that can be a whole extra gallon bought for nothing.
3. Forgetting the ceiling. If the ceiling is being painted, it is a full extra surface, in a 12 × 12 room it adds 144 sq ft.
4. Big colour changes without primer. Going from dark to light (or the other way) often needs a primer coat first. Primer is bought separately and is not in this answer.
Questions People Ask
How much paint do I need for a 12×12 room?
About 2 gallons for the walls with 2 coats (8 ft walls, 1 door, 1 window). The exact need is 1.99 gallons, so 2 whole gallons.
How much does one gallon of paint cover?
About 350 sq ft for one coat on a smooth wall, it is printed on the can. Rough walls and very dark colours cover less.
Do I need primer as well?
On new drywall, stained walls, or a big colour change, yes, a primer coat first makes the paint cover properly. Primer is extra and not counted here.
Should I buy a little extra paint?
Yes. Keep a small amount for touch-ups later. Buying the same colour again months later can look slightly different.
Can I use this for the outside of a house?
Yes, wall by wall: use each outside wall’s length and height, take off its doors and windows, and add the walls together. Siding with deep grooves needs more paint than the flat number.
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