How to Calculate How Much Paint to Buy

How to Calculate How Much Paint to Buy - How to Calculate How Much Paint to Buy

Avoid buying too much paint for your next interior, exterior, or bedroom painting project.  Overbuying means wasted money as unused cans dry up before you need them again. Learn how to calculate how much paint to buy from professional Brisbane painters.

Measure the Paintable Surface Area

The first thing you will need to do is calculate the surface area you plan to paint. This surface area should include all of the walls and even the doors if you plan to paint them. .

First, you will need to measure the length of each wall, and add them together. This is the perimeter of the room. Then, measure the height of the wall. Multiply the perimeter and the height, and you’ve calculated the total surface area of the walls in your room. To illustrate, imagine the perimeter of the room 12m, and the height of the walls is 2m.

12m x 2m = 24 metres squared

The total surface area of your room is 24 metres squared.

Next, consider the number of doors and windows. For each door, subtract 1.9 metres squared, and for each window, subtract 1.4 metres squared. Say this room has one door, and two windows. The total paintable surface can be calculated as follows:

Door and window surface area = (1 x 1.9) + (2 x 1.4)
= 4.7 metres squared

Total paintable surface = 24 – 4.7
= 19.3 metres squared

Estimate what you need

As a general rule, 1 litre of paint will cover between 6 and 6.5 metres squared of wall.

So, to calculate how many litres of paint you will need, divide the total paintable surface area by 6.5. Let’s return to the example above, and calculate how much paint is required.

Paint required = paintable surface area / 6.5
                         = 19.3 / 6.5
                         = 2.97 litres

For this example, you’ll need to purchase 3 litres of paint.

Other Considerations

There are a few things you’ll need to consider when calculating how much paint to buy.

  • Are you repainting a wall, or painting bare drywall? Drywall will absorb more paint, which means you’ll need to buy slightly more paint, even if you’ve coated it with a primer.
  • Are you painting in a light or dark colour? If you’re using a dark colour, you will probably require a tinted primer, too.
  • Don’t forget about future retouches. Always round the required amount of paint up, because you can use that paint in the future to touch up and remove stains and areas of wear and tear.

Here’s a Short Cut

Instead of making these calculations yourself, head over to the Dulux Paint Calculator. From there, simply type in your room’s dimension, the number of windows, and the number of doors and the calculator will do the work for you.

Professional Painters in Brisbane and Gold Coast

The easier option is to leave it all to us, the professional commercial painting and house painters Brisbane and Gold Coast locals trust. We can answer all of your questions, including how much paint to buy, how long does it take to paint a room, and more.

Contact us for a quick and accurate quote. Give us a call on 07 3829 5735 or fill out the form on this page.

Contact Us

Avatar for Louise Kraudelt

About Louise Kraudelt

Meet Louise Kraudelt, a knowledgeable and insightful author in the field of house painting. With a passion for sharing her expertise, Louise provides valuable information and tips on all aspects of commercial and house painting in this blog.


  1. Avatar for Ahmad Ahmad on 10/05/2020 at 6:57 am

    thanks for your illustrative article .. appreciated

  2. Avatar for hubert M Telan hubert M Telan on 03/26/2021 at 10:44 pm

    Thanks for your simple formula on how to calculate the paint to be used in a room, it serves as a guide.

  3. Avatar for Raj Singh Raj Singh on 04/29/2021 at 4:07 am

    Thank you for your guides. It’s well explained in simple easy way to understand.

  4. Avatar for Oyekunle Adekunle Amos Oyekunle Adekunle Amos on 05/03/2021 at 10:15 am

    Already solved the problem.

  5. Avatar for Onyinyechi Onyinyechi on 06/05/2021 at 9:36 pm

    Thanks for the article, it was a great help.

    • Avatar for Omeir muhudin farah guudlawe Omeir muhudin farah guudlawe on 07/31/2023 at 8:19 am

      Thanks 👍👍

  6. Avatar for Luabingi Luabingi on 06/06/2021 at 3:59 am

    Thank you for the helpful article with details.

  7. Avatar for Engr Morris Erobome Morris Engr Morris Erobome Morris on 09/21/2021 at 6:57 am

    I appreciate your kind perusal of how to calculate painting of buildings in square metres and the density to divide with thanks

  8. Avatar for Budri micheal Budri micheal on 10/19/2021 at 7:31 am

    Is that 6 – 6.5 metres square for one coat.

  9. Avatar for Lucifer Morningstar Lucifer Morningstar on 11/08/2021 at 1:01 pm

    How about primer?
    Is the quantity same for primer as well?
    And yes it that quantity for only one coat?

  10. Avatar for George George on 11/22/2021 at 4:13 am

    Is it 6m for each coat?

  11. Avatar for Lorenc Lorenc on 11/28/2021 at 9:28 am

    Thanks 6m one coat or no.

  12. Avatar for Gibson Macdonald Gibson Macdonald on 03/25/2022 at 7:27 am

    Thanks for your illustrations,my question is,is the 6.5 for one coat?

  13. Avatar for Flotia Chisale Flotia Chisale on 05/18/2022 at 7:14 am

    Very good explanation, I like it

  14. Avatar for thank you thank you on 06/02/2022 at 11:36 pm

    you saved me with my math assignment 🙂

  15. Avatar for Alfo Alfo on 09/07/2022 at 12:06 pm

    Thankyou so much!

  16. Avatar for Henry Henry on 11/20/2022 at 11:21 pm

    This is way too much – dulux say 15m2 per litre. As several people have asked already, do you mean 1 coat or 2/3?

  17. Avatar for Atex Onuger Atex Onuger on 01/05/2023 at 4:45 am

    its a helpful simple formula. problem solved. thankyou so much

  18. Avatar for Amir Shatalee Amir Shatalee on 01/18/2023 at 9:45 am

    How we have to calculate if we need to apply 3 coats ?

    I have to say thank you for help

  19. Avatar for Denis Duncan Denis Duncan on 09/08/2023 at 1:00 am

    A great formula. It’s always so hard to know the right amount and no over or under-buy. thanks


  20. Avatar for Akin Akin on 09/19/2023 at 3:16 pm

    Thanks for your simple explanation

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