Paint Calculator

What this paint calculator does

Enter your room's length, width, and wall height, and it works out how much paint you need — in gallons or liters — after deducting the space taken up by doors and windows and accounting for however many coats you're planning. It rounds up to real can sizes too, so you know exactly what to put in the cart instead of guessing and either running short mid-wall or overbuying.

Who it's for

Anyone repainting a bedroom, living room, or office who wants a real number before heading to the paint counter, rather than eyeballing it or relying on a vague "one gallon covers a small room" rule of thumb.

How to use it

• Enter the room's length, width, and wall height (feet or meters — the coverage rate switches to gallons or liters automatically).
• Set how many doors and windows the room has; the calculator subtracts their typical area from your total wall space automatically.
• Choose how many coats you're applying — most rooms need two for even coverage, especially over a different existing color.
• Optionally include the ceiling if you're painting that too, and adjust the coverage rate if your specific paint's label says something other than the 350 sq ft (or 10 sq m) per gallon default.
• Read off the total gallons or liters needed, plus how many 1-gallon or 5-gallon cans (or 1L/4L/10L cans) that works out to.

Real-world use cases

• Repainting a bedroom or living room: get an exact gallon count instead of buying "one can just in case" and ending up with unused paint.
• Painting a whole house: run the calculator room by room and add up the totals to place one big paint order.
• Budgeting a painting job: contractors and DIYers alike can estimate material cost before starting, based on can counts rather than rough area guesses.
• Deciding between a quart and a gallon for a small accent wall or closet, where a full gallon would be wasteful.

Frequently asked questions

How much paint do I need for a 12x10 room?

It depends on ceiling height, door/window count, and number of coats, but as a rough example: a 12x10 room with 8-foot walls, one door, and two windows needs roughly 1 gallon for a single coat, or about 2 gallons for two coats at standard coverage. Enter your exact numbers above for a precise figure.

Why does the calculator subtract area for doors and windows?

A standard interior door takes up about 21 sq ft (2 sq m) and a standard window about 15 sq ft (1.4 sq m) of what would otherwise be paintable wall — skipping this deduction is the single most common reason people overbuy paint.

How many coats of paint do I actually need?

Two coats is standard for most walls, especially with a color change or a lighter color going over a darker one. A single coat can work for a simple refresh in the same color, and very dark colors sometimes need three.

Does one gallon really cover 350 square feet?

That's the industry-standard estimate for a smooth, primed wall, but it varies by brand and paint type — textured walls, unprimed drywall, or very light colors covering dark ones typically get less coverage. Check your specific paint can's label and adjust the coverage field if it differs.

Should I include the ceiling in the same calculation?

Only if you're using the same paint on the ceiling and walls. Ceilings usually use a flat ceiling-specific paint, so for most rooms it's more accurate to run this calculator twice: once for the walls, once for the ceiling with the ceiling-only checkbox.