Paint Calculator
Paint = (Wall area × Coats) / Coverage
ConstructionHow to Use This Tool
Paint calculator
Enter the dimensions of your room to estimate how much paint you need. This calculator accounts for doors and windows so you only buy what the walls actually require. Below is a breakdown of coverage rates, how to measure your space, and tips for getting accurate estimates before you head to the store.
- Paint coverage by type
- How to measure your room
- Walls
- Subtract doors and windows
- Ceilings
- Trim and baseboards
- Example calculations
- Standard bedroom
- Living room
- Bathroom
- Factors that change how much paint you need
- Tips for buying paint
- Quick reference by room size
- Frequently asked questions
- How much does a gallon of paint cover?
- How many coats of paint do I need?
- Should I buy a gallon or a quart?
- How do I calculate paint for a ceiling?
- Does primer count as a coat?
- How much paint do I need for exterior walls?
- Related tools
- Measurement guides
Paint coverage by type
Coverage depends on the paint formula, the surface texture, and whether you are painting over a similar color or making a drastic change. The table below shows typical coverage for one coat on a smooth, primed surface.
| Paint type | Coverage per gallon | Coverage per liter |
|---|---|---|
| Interior latex (flat/matte) | 350 to 400 sq ft | 8.5 to 10 sq m |
| Interior latex (eggshell/satin) | 350 to 400 sq ft | 8.5 to 10 sq m |
| Interior latex (semi-gloss/gloss) | 300 to 350 sq ft | 7.5 to 8.5 sq m |
| Exterior latex | 250 to 350 sq ft | 6 to 8.5 sq m |
| Primer | 200 to 300 sq ft | 5 to 7.5 sq m |
| Oil-based/alkyd | 350 to 400 sq ft | 8.5 to 10 sq m |
Most projects need two coats for even coverage. The calculator defaults to two coats, but you can adjust this if you are applying a single maintenance coat over the same color.
How to measure your room
Walls
Measure the length of each wall in feet or meters. Multiply each length by the ceiling height to get the wall area. Add all four walls together for the total wall area. A room that measures 12 feet by 14 feet with 8-foot ceilings has a total wall area of (12 + 14 + 12 + 14) x 8 = 416 square feet.
Subtract doors and windows
A standard interior door is about 21 square feet (3 x 7 feet). A standard window is about 15 square feet (3 x 5 feet). Subtract these from the total wall area. The room above with two windows and one door would need paint for 416 – 15 – 15 – 21 = 365 square feet of wall surface.
Ceilings
If you are painting the ceiling, multiply the room length by the room width. The 12 x 14 foot room has a ceiling area of 168 square feet. Ceiling paint typically covers the same rate as flat wall paint.
Trim and baseboards
Measure the total length of trim in feet, then multiply by the trim height (usually 3 to 6 inches, or 0.25 to 0.5 feet). A room with 52 linear feet of 4-inch baseboard has about 17 square feet of trim to paint.
Example calculations
Standard bedroom
Room: 12 x 12 feet, 8-foot ceilings. Two windows, one door. Total wall area: (12 + 12 + 12 + 12) x 8 = 384 sq ft. Subtract openings: 384 – 15 – 15 – 21 = 333 sq ft. At 375 sq ft per gallon with two coats: 333 x 2 = 666 sq ft of coverage needed, so about 1.8 gallons. Buy 2 gallons.
Living room
Room: 18 x 22 feet, 9-foot ceilings. Four windows, two doors. Total wall area: (18 + 22 + 18 + 22) x 9 = 720 sq ft. Subtract openings: 720 – (4 x 15) – (2 x 21) = 720 – 60 – 42 = 618 sq ft. Two coats: 618 x 2 = 1,236 sq ft. At 375 sq ft per gallon: about 3.3 gallons. Buy 4 gallons.
Bathroom
Room: 8 x 6 feet, 8-foot ceilings. One window, one door. Total wall area: (8 + 6 + 8 + 6) x 8 = 224 sq ft. Subtract openings: 224 – 15 – 21 = 188 sq ft. Two coats: 376 sq ft. At 375 sq ft per gallon: about 1 gallon. A single gallon will be enough.
Factors that change how much paint you need
Surface texture makes a big difference. Textured walls, stucco, and rough plaster absorb more paint than smooth drywall. Expect 10 to 25 percent less coverage per gallon on textured surfaces.
Color changes matter. Going from a dark color to a light one (or the reverse) often requires an extra coat or a tinted primer. Painting white over dark red or navy blue can take three coats even with primer.
Unpainted or new drywall soaks up the first coat. Always prime new drywall before applying finish paint. Primer is cheaper than finish paint and creates a better base.
Application method affects waste. Rollers use paint efficiently. Brushes work well for cutting in edges. Sprayers cover large areas fast but can use 20 to 30 percent more paint due to overspray.
Tips for buying paint
- Buy slightly more than the calculator suggests. An extra quart covers touch-ups and mistakes without requiring a second trip. Most stores allow returns on unopened cans within 30 days.
- One gallon of paint weighs about 10 to 12 pounds. If you are carrying paint up stairs or across a job site, plan accordingly. Five-gallon buckets weigh 50 to 60 pounds.
- Store leftover paint in a cool, dry place with the lid sealed tightly. Latex paint lasts up to 10 years unopened and 2 to 5 years after opening if stored properly. Write the room name and date on the can.
- Ask the paint store to shake the can on their machine. Hand-stirring does not mix the pigment as thoroughly, especially with darker colors.
Quick reference by room size
These estimates assume 8-foot ceilings, smooth walls, standard door and window deductions, and two coats of latex paint at 375 sq ft per gallon.
| Room size | Wall area (approx) | Paint needed (2 coats) |
|---|---|---|
| 8 x 10 ft | 250 sq ft | 1.5 gallons |
| 10 x 12 ft | 300 sq ft | 2 gallons |
| 12 x 14 ft | 365 sq ft | 2 gallons |
| 14 x 16 ft | 430 sq ft | 2.5 gallons |
| 16 x 20 ft | 510 sq ft | 3 gallons |
| 18 x 22 ft | 618 sq ft | 4 gallons |
| 20 x 24 ft | 700 sq ft | 4 gallons |
Frequently asked questions
How much does a gallon of paint cover?
A gallon of interior latex paint covers 350 to 400 square feet on a smooth surface in one coat. That is roughly a 10 x 10 foot room (walls only). Two coats cut the effective coverage in half.
How many coats of paint do I need?
Two coats is standard for most jobs. You may get away with one coat if you are painting the same color or using a paint-and-primer combo over a light base. Dark-to-light color changes may need three coats.
Should I buy a gallon or a quart?
A quart covers about 90 to 100 square feet per coat. It works for accent walls, small bathrooms, or trim. For anything larger, gallons are more cost-effective per square foot.
How do I calculate paint for a ceiling?
Multiply the room length by the room width. A 12 x 15 foot room has 180 square feet of ceiling. One gallon covers it in two coats with some left over.
Does primer count as a coat?
No. Primer prepares the surface but does not replace a finish coat. After priming, you still need one or two coats of your finish color. Primer typically covers 200 to 300 square feet per gallon.
How much paint do I need for exterior walls?
Exterior paint covers less per gallon (250 to 350 sq ft) because outside surfaces tend to be rougher. Measure the height and width of each wall, subtract windows and doors, and plan for two coats.
Related tools
Measurement guides
Formula & Explanation
The calculator computes wall area as perimeter × height. It does not subtract doors and windows automatically — subtract approximately 1.5 m² per standard door and 1 m² per standard window for a more accurate estimate.