Running out of paint mid-project is one of the most avoidable decorating disasters. Yet it happens constantly — usually because someone guessed at the gallons while standing in the store aisle. Our free paint calculator takes the guesswork out entirely: enter your room dimensions and get an exact estimate of how much paint you actually need.

The math matters more than most people think. Two coats are standard for a rich, even finish, and doors, windows, and trim all change the equation. Buy too little and you’ll be racing back to the store mid-weekend; buy too much and you’ve wasted money on gallons that will sit in the garage for years. For a second opinion, compare your result with Benjamin Moore’s paint calculator.

How the paint calculator works

Enter your room’s length, width, and ceiling height, add the number of doors and windows, and the calculator instantly estimates the gallons needed for two full coats. It uses realistic coverage rates — not the optimistic numbers on the can — so your estimate holds up in the real world. Painting just one accent wall? Measure that wall alone for a precise single-wall figure.

Buy smart, paint once

Once you have your number, order everything at once so all gallons come from the same batch — color can vary slightly between batches. And if you’re still choosing a shade, our guide on creating a sophisticated neutral interior shows how the right paint color can completely transform a room. Good prep, quality paint, and the right quantity: that’s the whole secret to a flawless finish.

Measure twice, buy once — your walls will thank you.

Paint calculator FAQs

How many coats of paint should I calculate for? Plan for two coats — the standard for a rich, even finish. One-coat coverage claims rarely hold up on real walls.

Does the paint calculator account for doors and windows? Yes. Enter the number of doors and windows and the calculator subtracts their area so you don’t overbuy.

Should I buy extra paint beyond the estimate? Round up to the nearest gallon and keep a small amount sealed for touch-ups — stored at room temperature, it lasts for years.