How much paint do you need for a room? This free paint calculator works out the exact gallons (and liters) for your walls and ceiling, subtracts doors and windows, and tells you which cans to buy, how much primer you need, the total cost and how long the job will take. Pick a color to preview it on the walls.
Paint Calculator
Exact gallons, cans, primer and cost for any room, with a live color preview.
Coverage: 400 sq ft per gallon on smooth walls (about 10 m² per liter). Each door subtracts 20 sq ft and each window 15 sq ft. Always check the coverage printed on your paint can.
How to Use the Paint Calculator
- Enter the room length, width and wall height in feet or meters.
- Add the number of doors and windows so their area is subtracted.
- Choose how many coats you will apply and your wall surface type.
- Decide whether to include the ceiling and a coat of primer.
- Set your paint price per gallon to see the total cost, then copy the shopping list.
How Much Paint Do I Need? The Formula
Wall area = 2 × (length + width) × height − doors − windows
Gallons of paint = wall area × number of coats ÷ coverage per gallon
One gallon of interior paint covers about 350 to 400 sq ft on smooth walls (roughly 9 to 10 m² per liter). Textured and porous surfaces drink more paint, so coverage falls to around 300 sq ft per gallon.
Example: a 14 × 12 ft bedroom with 8 ft walls has 416 sq ft of wall. Subtract one door (20 sq ft) and two windows (30 sq ft) to get 366 sq ft. Two coats is 732 sq ft, so you need about 1.8 gallons: buy two 1-gallon cans.
Paint Needed by Room Size
| Room size (8 ft walls) | Wall area | Paint for 2 coats |
|---|---|---|
| 10 × 10 ft (small bedroom) | ~270 sq ft | 1.5 gallons |
| 12 × 12 ft | ~330 sq ft | 1.75 gallons |
| 14 × 12 ft | ~366 sq ft | 2 gallons |
| 16 × 14 ft (living room) | ~430 sq ft | 2.25 gallons |
| 20 × 15 ft | ~510 sq ft | 2.75 gallons |
Figures assume one door and two windows and smooth walls.
How Much Does a Gallon of Paint Cost in 2026?
Budget interior paint costs around $20 to $35 a gallon, mid-range paint $35 to $55, and premium paint-and-primer lines $55 to $90 or more. Five-gallon buckets usually work out 10 to 20% cheaper per gallon. Use the price slider in the calculator to match the paint you are looking at.
Do You Need Primer?
- Yes for new drywall, bare plaster, wood, patched areas, stains, or a big color change (dark to light or light to dark).
- Usually no if you are repainting a clean wall in a similar color with a quality paint-and-primer product.
- One gallon of primer covers about 200 to 300 sq ft.
Painting Tips for a Better Finish
- Pick the right sheen: flat or matte for ceilings, eggshell for living rooms and bedrooms, satin or semi-gloss for kitchens, bathrooms and trim.
- Cut in edges with a brush first, then roll walls in a “W” pattern while the edges are still wet.
- Wait the full recoat time on the can, usually 2 to 4 hours, before the second coat.
- Pair a fresh color with the right light. Our lumens calculator shows how bright each room should be.
Frequently Asked Questions
How much paint do I need for a 12×12 room?
A 12×12 room with 8 ft walls has about 330 sq ft of paintable wall after subtracting a door and two windows. For two coats you need about 1.75 gallons, so buy two 1-gallon cans.
How many square feet does a gallon of paint cover?
One gallon covers about 350 to 400 sq ft of smooth wall per coat. On textured walls, brick or new plaster, plan for about 300 sq ft per gallon.
Do I need 2 coats of paint?
Two coats are recommended for most walls. They give even color, hide roller marks and last longer. Dark or bold colors and big color changes almost always need two coats.
How much paint do I need for a ceiling?
Multiply the room length by width. A 12×12 ceiling is 144 sq ft, which needs under half a gallon per coat, so one gallon is enough for two coats.
How many liters of paint do I need per square meter?
One liter of paint covers about 10 m² per coat on smooth walls. A room with 40 m² of wall needs about 8 liters for two coats.
More Free Home Calculators
- Square Footage Calculator – area of any room or floor plus flooring cost
- Lumens Calculator – how many bulbs and lumens each room needs
- Smart Home Cost Calculator – budget for a full smart home setup
- Power Station Runtime Calculator – how long a battery backup will run your devices
- AC BTU Calculator – find the right air conditioner size for any room
