Room paint calculator
Estimate wall paint from room perimeter, wall height, openings, coats, and coverage rate.
How paint estimates work
Paint is normally estimated by surface area and coats. For a simple room, wall area is room perimeter multiplied by wall height, minus a reasonable allowance for doors and windows. Multiply the remaining wall area by the number of coats, then divide by the coverage rate listed on the paint can.
The result is a planning number, not a guarantee. Paint coverage changes with color change, primer, wall texture, roller nap, drywall condition, patching, and whether the surface is sealed. Dark colors, bright colors, and porous surfaces can require more paint than the label average.
What to measure
- Measure the total wall perimeter, not just one wall.
- Use actual wall height if ceilings are taller or shorter than 8 feet.
- Subtract large openings if you want a closer estimate.
- Include a second coat when changing colors or painting repaired walls.
- Use the coverage number from the specific paint product.
Primer and color changes
Primer is not always the same as paint coverage. A patched wall, fresh drywall, water stain, strong previous color, or glossy surface may need primer before paint. If primer is needed, estimate it separately using the primer label coverage. This makes the shopping list clearer and helps avoid trying to solve coverage problems with extra finish paint.
Common mistakes
People often forget closets, short return walls, stair walls, or accent walls. They also forget that two coats doubles the square footage covered. Another mistake is buying only the exact calculated amount when the project includes touch-ups, cutting in, spills, or future repairs.
Example
A 12-by-14 room has a perimeter of 52 feet. With 8-foot walls, that is 416 square feet before openings. Subtract 60 square feet for doors and windows and the paintable area is 356 square feet. Two coats require 712 square feet of coverage. At 350 square feet per gallon, the homeowner should plan around 3 gallons.
Frequently asked questions
Should I subtract windows and doors?
Yes for a closer estimate, especially if the room has large windows or multiple doors.
Does primer count as a coat?
Primer should usually be estimated separately using the primer product coverage.
Why did I use more paint than estimated?
Texture, repairs, porous surfaces, dramatic color changes, and application method can reduce real coverage.
Paint formula explained
Room paint estimates start with wall area. A simple rectangular room uses perimeter multiplied by wall height. The calculator then subtracts common openings if entered, multiplies by the number of coats, and divides by the coverage rate listed on the paint can. The result is rounded for buying full gallons.
Coverage varies by paint, wall texture, color change, primer, and surface condition. A smooth wall painted a similar color may cover better than a rough wall going from dark to light. Use the coverage number from the exact product when possible instead of assuming every gallon covers the same area.
Openings, trim, and ceilings
Doors and windows reduce wall paint area, but trim, closets, accent walls, and touch-ups can add paint needs back in. Ceilings are usually estimated separately because ceiling paint, sheen, and coverage may differ from wall paint. If the ceiling is included, calculate it as length multiplied by width and add it to the paint plan.
Buying notes
It is often practical to have a little paint left for touch-ups, especially in high-traffic rooms. At the same time, buying far more than needed wastes money and storage space. Keep the label, color code, sheen, and room name with any leftover paint so future touch-ups are easier.
Example room estimate
A 12 by 14 room with 8-foot walls has a perimeter of 52 feet. The wall area is about 416 square feet before subtracting openings. Two coats would require coverage for about 832 square feet before waste. If the paint covers 350 square feet per gallon, the project may need about three gallons after rounding.
Surface condition check
Patched drywall, fresh joint compound, stains, smoke residue, glossy paint, and rough texture can change paint needs. Clean, repair, sand, and prime where appropriate before relying on a final gallon count. Better preparation often matters as much as buying enough paint.