Buying the wrong amount of paint means either an inconvenient extra trip to the store or leftover paint going to waste — this calculator works out exactly how many gallons you need based on your actual wall area.
Enter your room's length, width, and wall height to calculate total wall surface area, subtract space for doors and windows, and multiply by your number of coats — the tool then converts that into gallons needed, using the standard coverage assumption of about 350 square feet per gallon.
Buying slightly more than the calculated amount is generally wise for touch-ups later, since paint colors can be difficult to exactly match if you run out and need to remix a batch.
Because everything runs locally in your browser, results appear instantly and nothing you type or upload is ever sent to a server.
Bookmark this page if you expect to use this tool regularly — it loads fast and behaves the same way every time, with no account needed.
This kind of task shows up constantly in everyday writing, coding, design, and admin work, which is exactly why a dedicated, focused tool saves so much back-and-forth.
A tool that does one job well, without a cluttered interface or unrelated features competing for attention, tends to be faster to use than a heavier all-in-one app.
If you find yourself needing this often, keeping this page open in a tab is usually faster than digging through a bigger software suite's menus.
Because there's no sign-up or installation step, you can jump straight from a search result to a working tool in a couple of seconds.
Frequently asked questions
How much area does one gallon of paint cover?
Most standard paints cover approximately 350-400 square feet per gallon per coat; this calculator uses 350 as a conservative standard estimate.
Should I round up the gallon estimate?
Yes, it's generally wise to round up to the next full gallon or even buy a little extra, since running short mid-project is more inconvenient than having a bit left over.