WorldCalcs

Paint Calculator

How much paint do I need? Estimate gallons or liters for any room.

Reviewed by the WorldCalcs team · Methodology · Last reviewed: June 2026

Paint needed

1.81 gallons

Round up to buy: 2 gallons

Wall area
352.00 sq ft
Area deducted (doors + windows)
36.00 sq ft
Paintable area
316.00 sq ft
Total area to cover (× coats)
632.00 sq ft

These results are estimates only. Coverage rates and bag yields vary by product, surface, and conditions - always round up, buy a little extra, and confirm quantities with your supplier. See our disclaimer.

What is a paint calculator?

A paint calculator estimates how much paint you need to cover the walls of a room. It adds up your wall area, subtracts the space taken by doors and windows, multiplies by the number of coats, and divides by how much area one gallon (or liter) of paint covers. The result tells you how many gallons or liters to buy so you don't run out halfway - or overspend on cans you'll never open.

How paint is calculated

First we find the total wall area: 2 x (length + width) x ceiling height. A standard interior door takes about 21 sq ft (1.9 m2) and a standard window about 15 sq ft (1.4 m2), so we subtract those to get the paintable area. Multiply by the number of coats - most jobs need two - then divide by the paint's coverage rate. A gallon typically covers about 350 sq ft per coat; a liter covers roughly 10 m2. Because you can only buy whole cans, we round up.

Example

For a 12 ft x 10 ft room with an 8 ft ceiling, one door and one window, painted with two coats: the walls are 352 sq ft, minus 36 sq ft for the openings leaves 316 sq ft of paintable surface. Two coats means 632 sq ft to cover. At 350 sq ft per gallon that's 1.81 gallons - so you'd buy 2 gallons.

Need to measure your floor first? Try our Square Footage Calculator. Planning more home projects? See the Concrete Calculator and Tile Calculator.

All calculations happen in your browser. Nothing is sent, stored, or tracked.

Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer

How to use

Pick imperial (feet, gallons) or metric (meters, liters). Enter the room's length, width and ceiling height, the number of doors and windows, and how many coats you plan to paint. The coverage field defaults to 350 sq ft per gallon or 10 m² per liter — adjust to match your paint can if needed.

The result shows the paintable wall area, the total area to cover (after multiplying by coats), how much paint that needs, and a rounded-up number of cans to buy.

Frequently asked questions

How much paint do I need for a room?+

Measure the room's length, width and ceiling height, calculate the wall area, subtract doors and windows, and multiply by the number of coats. A typical 12x10 ft room needs about 2 gallons for two coats. Enter your numbers above for an exact figure.

How much does a gallon of paint cover?+

One gallon covers roughly 350 sq ft per coat on smooth interior walls - about the walls of a small bedroom. Rough, porous or dark-to-light surfaces cover less, so check the can and round up.

How many coats of paint do I need?+

Two coats is standard for an even finish and full coverage. You may get away with one coat when repainting a similar color, but big color changes - or covering a dark wall - often need two or even three.

Do I subtract doors and windows?+

Yes. This calculator subtracts about 21 sq ft per door and 15 sq ft per window so you don't pay for paint you won't use. For very large windows or sliding doors, measure them and adjust.

How do I calculate paint for a ceiling?+

A ceiling's area is simply its length x width. Add that to your wall area if you're painting the ceiling too, then divide by the coverage rate as usual.

How much paint for 1,000 square feet of wall?+

At 350 sq ft per gallon you'd need about 2.9 gallons per coat, or roughly 5.7 gallons for two coats - so plan on 6 gallons.

Does this include primer?+

No - primer is a separate product with its own coverage. If you're priming bare or patched walls, buy primer separately and use the same method (area / coverage) to estimate it.

How do I work it out in liters?+

Switch the calculator to meters. It then uses square meters for area and a coverage of about 10 m2 per liter, giving you the number of liters to buy.

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