Paint Calculator

Enter room size and openings. Pick coats and coverage. We give gallons, liters, and the cheapest mix of 5-gallon, 1-gallon, and quarts.

Estimate paint like a pro—without the guesswork

Getting paint right is part math, part experience. This calculator handles the math so your experience can focus on finish and color. Feed it your room dimensions, how many doors and windows you’ll subtract, and the number of coats you want. If you’re priming, add primer coats and coverage separately. We’ll total wall and ceiling area, add a sensible overage for cut-ins and roller loss, and convert everything into gallons and liters. You also get a shopping plan: the best mix of 5-gallon buckets, single gallons, and quarts to cover the job with minimal leftovers—plus optional price fields if you want a quick budget.

Coverage numbers vary a lot between brands and surfaces. Smooth, previously-painted walls might hit 400 sq ft per gallon; new drywall or dark-to-light changes are often closer to 250–300. If you’re not sure, start conservative and adjust. For planning a whole project, the Square Footage Calculator can help estimate flooring or trim, and the Drywall Calculator pairs nicely with primer decisions.

Settings

US: sq ft per gallon (typical 300 to 400)
US: sq ft per gallon

Room

Openings

US: 21 sq ft per door
US: 15 sq ft per window

How to use this paint calculator

  1. Pick your unit system. US uses feet and gallons; Metric uses meters and liters. Hints and defaults change automatically so you don’t have to convert in your head.
  2. Set waste/overage. 10% is a practical default for cut-ins, roller loss, and touch-ups. New drywall or heavy texture? Bump it up.
  3. Choose coats. Enter wall and ceiling coats separately. If you’re priming, switch “Use primer” to Yes and enter primer coats too.
  4. Adjust coverage. Use the numbers on the can if you have them. Otherwise 300–400 sq ft/gal (8–12 m²/L) is typical for paint; primer is often a bit lower.
  5. Room mode: Enter length, width, height, and whether to include the ceiling. Add doors and windows so we subtract that area from the walls.
  6. Custom mode: Handy for accent walls, stairwells, or outdoor pieces. Add each area directly in ft² or m².
  7. Optional pricing. Drop in prices for 5-gal, 1-gal, and quarts (and primer equivalents). We’ll search the cheapest mix that meets coverage with minimal leftovers.
  8. Export if needed. Click CSV to stash the plan in your project folder or share with a contractor.

Reading the results (and dialing them in)

Total paint/primer area multiplies surfaces by coats, then adds your waste percentage. That’s the number most people underestimate. If you’re changing from navy to white, expect more coats or a high-hide primer.

Gallons vs. liters are both shown so you can shop anywhere. The calculator never rounds down coverage; if we’re between sizes, it rounds the purchase up to ensure you don’t run dry with one wall left.

Packaging and cost tries combinations of buckets, gallons, and quarts to cover the job. If you don’t enter prices, we still propose a sensible mix; add pricing to get an estimated total and spot where 5-gallon buckets are worth it.

Reality check: rough or porous surfaces, heavy texture, or fresh drywall can drink paint. When in doubt, add a quart or a spare gallon—unused, unopened paint is easier than a second store run mid-project.

Working out trim, tile, or board feet next? Try our Tiles Calculator, Drywall Calculator, or the general-purpose Square Footage Calculator.

FAQ

What coverage should I use if the can lists a range?

Use the lower number if the surface is rough, newly primed, or you’re covering a high-contrast color. Use the higher number for smooth, previously painted walls.

Do I need primer?

Yes for new drywall, major color changes, stains, or glossy surfaces you’ve just scuff-sanded. Otherwise quality paints can self-prime in two coats—still, the separate primer option here lets you choose.

Why include waste?

Cut edges, roller loading, and touch-ups all consume paint. A 5–15% buffer prevents coming up short. You can always keep an unopened gallon for returns (store policy permitting).

How accurate is the packaging optimizer?

It brute-forces small combinations to find the cheapest mix at or above your need. Prices change, so treat the total as directional and sanity-check at your store.