Paint Calculator
Find out how much paint you need for a room before you head to the store. Enter the room's dimensions, how many doors and windows to skip, and the number of coats — you'll get the paintable wall area and how many gallons or liters to buy. Updates as you type.
How it works
paint = (wall area − doors − windows) × coats ÷ coverage
- Wall area = perimeter × height = 2 × (length + width) × height — the four walls.
- Openings are subtracted using typical sizes: a door ≈ 21 sq ft (1.9 m²), a window ≈ 15 sq ft (1.4 m²).
- Coverage defaults to 350 sq ft per gallon (11 m² per liter) per coat — change it to match your can.
- Cans to buy rounds up, because paint comes in whole cans and running out risks a colour mismatch.
Painting the ceiling too? Add its area (length × width) as a separate job, or run a second calculation for it.
FAQ
How do I calculate how much paint I need?
Add up the wall area (perimeter × wall height), subtract the doors and windows, then multiply by the number of coats. Divide that by the coverage rate of your paint (typically about 350 sq ft or 11 m² per coat per gallon/liter). This calculator does it all for you and rounds up to whole cans.
How much does one gallon of paint cover?
A US gallon usually covers about 350–400 square feet in one coat on a smooth, primed wall. One liter covers roughly 10–12 square meters. Rough, porous, or dark-to-light surfaces use more, so check the figure printed on your can and adjust the coverage field.
How many coats of paint do I need?
Two coats is the standard for an even, durable finish and is the default here. One coat may do for a same-colour refresh; three is sometimes needed when going from a dark colour to a light one or over bare drywall. Change the coats field to match your job.
Does this include the ceiling?
No — by default it estimates the four walls only, which is the most common painting job. To include a ceiling, add its area (room length × width) to the job separately, or treat it as its own calculation using the same coverage rate.
Why does it round up the number of cans?
Paint is sold in whole cans, and running out mid-wall means a trip back to the store and a possible batch-colour mismatch. The "cans to buy" figure rounds up so you have enough; the "paint needed" figure shows the exact amount for reference.
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