Paint Coverage Calculator
Enter your room's dimensions and coat count to find the net paintable area and how many gallons to buy.
Paint needed
How the estimate works
The calculator finds the gross wall area from your room's perimeter and ceiling height (2 × (length + width) × height), subtracts a standard allowance for the doors and windows you enter, then multiplies the result by your number of coats. Dividing that total by your coverage rate gives the exact gallons required, which is then rounded up to the nearest quarter gallon so it matches how paint is actually sold.
This is a planning estimate, not a precise order form — texture, porosity, and the color change you're making all shift real-world coverage. When in doubt, round up rather than down; running short mid-coat is more annoying than having a partial can left over.
Frequently Asked Questions
How much wall area does a gallon of paint cover?
Most interior paints cover roughly 300–400 square feet per gallon on a primed, smooth wall — this calculator defaults to 350 sq ft, the middle of that range. Textured walls, unprimed drywall, and dark-to-light color changes all reduce real coverage, so check the number printed on your own paint can and adjust the coverage field if it differs.
Why does the calculator subtract area for doors and windows?
You don't paint over doors and windows, so their area shouldn't count toward how much paint you buy. The calculator deducts a standard 21 sq ft per door and 15 sq ft per window from the gross wall area — close enough for planning purposes even though actual door and window sizes vary a little.
Why round up to the nearest quarter gallon?
Paint is typically sold by the gallon or the quart, so a result like 1.72 gallons isn't something you can buy exactly. The calculator rounds the exact figure up to the nearest quarter-gallon (quart) increment so you know what to actually purchase, with a small buffer for touch-ups and uneven spread.
Should I buy extra for a second coat or future touch-ups?
The coats field already multiplies the area by however many coats you plan to apply, so a 2-coat job is counted as double the area. It's still worth keeping a little extra paint on hand afterward for scuffs and touch-ups — a labeled leftover can, even a partial one, saves a repeat trip to color-match later.
Planning estimate only. Coverage varies by paint, surface texture, and application method — check your paint can's label and buy a little extra for touch-ups.