How to Calculate Paint Quantities

6th October 2021

We answer the question: how much paint do I need? with our guide on how to calculate paint quantities.

Working out your requirements for paint allows you to keep costs down and it ensures continuity of colour. Take a look at our step-by-step instructions for working out how much paint you need...

1. Measure Your Room

First, you will need to measure each wall you wish to paint. Use a metal ruler to measure the width and height in metres, then multiply each wall's width by its height.


Wall size: Height: 1.2m x Width: 2.4m = 2.88 square metres.

Take all the results from each wall you wish to paint and add them together. This will calculate the overall square metre measurement.

How To Calculate Paint Quantities How To Calculate Paint Quantities
How To Calculate Paint Quantities How To Calculate Paint Quantities

2. Subtract Windows and Doors

If you have large spaces that aren’t being painted, you should subtract this from your current total. This includes windows, doors and/or fireplaces.

Use the same calculation method as above to work out the total area. Then subtract it from your previous overall total.


Window size: Width: 0.35m x Height: 0.60m = 0.21 metres.

Wall total: 2.88m – 0.21m = 2.67 square metres.

3. Factor In Coats Of Paint

Multiply your new total square metre measurement by the number of coats you’ll need. We recommend applying at least two coats and it's also worth including a little extra paint for touch-ups.


Two coats x 2.67m = 5.34 square metres.

How To Calculate Paint Quantities How To Calculate Paint Quantities
How To Calculate Paint Quantities How To Calculate Paint Quantities

4. Calculate Your Total

Finally, divide this total figure by the m²/l number on your paint tin. This will give you the total litres of paint you need for your project.

Now you know how to calculate paint quantity for any room.


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