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Paint Calculator

Work out how much wall paint a room needs from its size or wall area, the number of coats, and the coverage on your paint can, with doors and windows deducted.

Units

Wall area

Coats and coverage

Coverage is printed on the paint can. Around 350 sq ft per gal is typical for one coat on a smooth wall.

Doors and windows

Assumes 21 sq ft per door and 15 sq ft per window. Everything runs in your browser. Nothing is uploaded.

Paint needed
1.9 gallons
for 2 coats over 333 sq ft of wall
2 gal
Buy at least
333 sq ft
Paintable area
666 sq ft
Area to cover (2×)
384 sq ft
Wall area
51 sq ft
Openings (1d, 2w)

This is an estimate. Texture, absorbency, and strong color changes can raise the real amount, so keeping a little extra for touch-ups is sensible.

How to calculate how much paint you need

  1. Choose your units

    Pick meters with liters or feet with gallons so every measurement and result uses the same system.

  2. Enter the wall area

    Type the room length, width, and wall height, or switch to enter a total wall area you already measured.

  3. Set coats and coverage

    Enter the number of coats and how much area one liter or gallon covers, taken from your paint can label.

  4. Deduct doors and windows

    Count the doors and windows to subtract their area, then read the paint needed and how much to buy.

Why use this tool

Room size or wall area

Enter length, width, and wall height and the perimeter method works out the wall area for you, or type a total area you have already measured.

Coats and coverage

Set any number of coats and the coverage printed on your paint can, so the estimate matches the exact product you plan to use.

Doors and windows deducted

Count the doors and windows in the room and their area is subtracted from the walls, so you do not buy paint for surfaces you will not cover.

Liters or gallons

Switch between meters with liters and feet with gallons at any time. Your measurements convert automatically so the result stays the same.

Buy the right amount

Alongside the exact paint needed, the tool rounds up to a sensible purchase amount so you leave the shop with enough to finish the job.

Runs entirely in your browser

Every calculation happens on your device as you type. Nothing is uploaded, stored, or logged.

About this tool

This paint calculator estimates how much wall paint a room needs and how much to buy. Give it the room size or a wall area you have already measured, the number of coats, and the coverage figure from your paint can, and it works out the paintable surface and the volume of paint required. When you enter room dimensions it treats the four walls as the room perimeter multiplied by the wall height, which is the standard way to size a rectangular room, then subtracts a typical area for every door and window you count so you are not paying to paint openings.

Work in meters and liters or in feet and gallons, and switch between the two at any point; your measurements convert automatically so the result never changes. Coverage varies by paint, surface, and color, so the coverage box is yours to edit: a smooth primed wall stretches a can further than bare plaster or a dark color going lighter, and a second coat almost always uses less than the first. The tool also rounds the exact figure up to a practical amount to buy, since paint is sold in whole cans. For converting odd measurements or comparing can sizes the unit converter helps, and the percentage calculator is handy for adding a waste allowance on top.

Treat the number as a close estimate rather than an exact order. Texture, absorbency, application method, and how many coats a strong color really needs all move the real total, so buying a little extra for touch-ups is sensible. Every calculation runs in your browser as you type, and nothing you enter is uploaded, stored, or logged.

Frequently asked questions

How does the paint calculator work?
From room dimensions it takes the perimeter, twice the length plus the width, and multiplies by the wall height to get the wall area. It subtracts a standard area for each door and window, multiplies the remaining area by the number of coats, then divides by the coverage per liter or gallon to get the paint needed.
How much does a liter or gallon of paint cover?
It depends on the paint and the surface, so the coverage field is editable. A common starting point is about 10 square meters per liter, or roughly 350 square feet per gallon, for one coat on a smooth, primed wall. Bare or textured surfaces soak up more, so use the figure on your can.
Can I enter the wall area directly instead of room dimensions?
Yes. Switch the input method to total wall area and type the number you measured, in square meters or square feet. This is useful for irregular rooms, sloped ceilings, or when you only want to paint some of the walls.
How are doors and windows handled?
Each door and window you count is subtracted using a typical size, about 1.9 square meters (21 square feet) per door and 1.4 square meters (15 square feet) per window. If your openings are much larger or smaller, switch to entering the wall area directly and subtract your own figures.
Why should I buy a bit more paint than the estimate?
The estimate assumes even coverage, but texture, absorbency, and strong color changes can raise the real amount, and touch-ups need a little in reserve. The tool rounds the exact figure up to a practical purchase amount, and buying one extra can is a safe habit.
Is my data uploaded anywhere?
No. Every measurement and result stays on your device. All calculations run in your browser as you type and nothing is sent to a server, stored, or logged.

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