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Paint Calculator: How Much Paint Do You Need?

This free paint calculator works out how many litres of paint you need for the walls of a room. It subtracts doors and windows, multiplies by the number of coats and adds a small allowance for waste.

By Debmedia Technologies LLP · Kolkata, India · Updated

What Is It and When Do You Need It?

Buying the right amount of paint saves money and avoids a second shop run. Too little leaves a wall unfinished with a color that may not match later, and too much is wasted money.

Enter the room size, doors, windows, coats and the coverage printed on the tin. The tool gives the litres to buy.

How to Use This Tool

  1. Enter the room length, width and wall height in metres.
  2. Enter the number of doors and windows.
  3. Enter the coats and the coverage from the tin.
  4. Press Calculate.

How the Calculation Works

Wall area = 2 × (length + width) × height. A door is taken as 1.9 m² and a window as 1.5 m². Paintable area = wall area − openings. Litres = paintable area × coats ÷ coverage, plus 10 percent for waste, rounded to the nearest tenth of a litre.

Worked Example

A room 5 m by 4 m with 2.7 m high walls has 48.6 m² of wall. With 1 door and 2 windows (4.9 m²), that leaves 43.7 m². Two coats at 10 m² per litre need 8.7 litres, or about 9.6 litres with waste.

Common Uses

  • Painting a room.
  • Budgeting a decorating job.
  • Comparing paints by coverage.
  • Checking a quote.

Tips and Common Mistakes

  • Add the ceiling area if you are painting it.
  • Rough or porous walls use more paint.
  • Buy all the paint at once so the color matches.

Next, you may need the tile calculator, concrete calculator, area calculator, volume calculator.

Everything runs in your browser. Nothing you type is uploaded, stored or sent to any outside service.

Frequently Asked Questions

Add the length and width, double it, and multiply by the wall height. Then subtract doors and windows.
Most emulsion paints cover about 10 to 12 square metres per litre for one coat. The tin tells you the exact figure.
Two coats are normal. Going from a dark to a light color may need three, and fresh plaster needs a primer or a thinned first coat.
No. Add the ceiling area (length × width) separately if you are painting it.

Disclaimer: results are calculated in your browser from the numbers you enter. Check important results before you rely on them for money, health, safety or legal decisions.