How to test a spirit level for accuracy

A spirit level bubble is a very useful piece of measuring equipment. For a spirit level to be useful it needs to be 100-per cent accurate. There is a very easy way you can check your spirit level for accuracy. You need to check your spirit level 4 level which is the horizontal plane and also plumb which is the vertical plane.  

  • Level refers to the horizontal plane from right to left or one end to the other such as a tabletop. 
  • Plumb refers to the vertical surface another word top to bottom.

Some levels have a 45-degree spirit vial. It is possible to check a 45-degree spirit vial for accuracy and I will explain in this blog.

This image shows a spirit bubble level with a rotating vial. This spirit level can be set for multiple angles and well suited to scaffolders.

Adjust a spirit level by calibrating it if the level has that facility. But first you need to use the methods below to test you spirit level for accuracy.

For testing a spirit level for level and plumb you will need

  • a flat surface
  • a vertical surface
  • a pencil or dry wipe pen

A step-by-step guide to checking the LEVEL accuracy of a spirit level

  1. Place level on a flat surface
  2. draw a line along with the level and at each end
  3.  Inspect the spirit bubble
  4.  Mark the ends of the spirit bubble with a pencil
  5.  pick up a spirit level and turn around end for end
  6.  put level down onto the flat surface
  7.  along with the pencil marks you drew on that flat surface
  8.  inspect the spirit bubble once more
  9.  if your spirit bubble is in the same position as it was the first time your level is accurate
  10. test your spirit level regularly.


A step-by-step guide to checking the PLUMB accuracy of your spirit level

  1. Place Your spirit level on to a vertical surface
  2. Mark the end and along with your spirit level
  3. using your soft pencil Mark the position of the bubble
  4. put away the spirit level from the vertical surface
  5. turn level from edge to edge
  6. again use a soft pencil and Mark the position of the spirit level bubble
  7. inspect the spirit level bubble and is it in the same position as it was the last time
  8.  if the bubble is in the same position as before your level is accurate
  9.  yet again don’t forget to check your spirit level regularly

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Our video on testing the spirit level for trueness

Watch this video to see for yourself how to test a spirit level for accuracy. It is a bit to the point but it has the direction needed to help you understand the methods of testing a spirit level.

Remember to check your spirit lebvels for accuracy often.

Testing The 45-degree  Vial on a spirit level

If your spirit level has a 45-degree vile and you wish to test it for true there is a way. I will try to explain to you how you can check the 45 degrees on your spirit level. you will require another piece of equipment to test the 45 degrees on a level.

What you will need for testing the 45 degrees vial

  • A vertical board or wall
  • A framing square
  • A pencil


A step-by-step guide to checking the 45° accuracy of your spirit level

  1. Hold a level against the wall on its side
  2. position level so it is at 45 degrees 
  3. align the bubble so it is is exactly in the middle
  4. draw a line on the wall
  5. reposition the level in a mirror image
  6. position that level so it is that 45 degrees
  7. align the bubble so it’s exactly in the middle
  8. check that the end of the level crosses over your previous pencil line
  9. you should at this point of drawn a 90 degree right angle
  10. put Level too one side
  11. use the framing Square and check the pencil-drawn 90 degree
  12. if the right angle is 100% 90 degrees
  13. then your 45-degree level is true

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Just like a square you can easily check that your spirit level is level and Plumb. Any tool for the checking of surfaces for either level plum or Square are required tools that are accurate. When you first buy your first spirit level it should be factory set and tested. In time I’m with your nice shiny level been thrown into a tool bag or box and used on-site in a less than careful manner. It is quite likely that the level might be knocked out of level or Plumb.

You can buy a Spirit Level in the USA on by clicking on these links

You can buy a Spirit Level in the UK on by clicking on these links

By Marcus Kett, Woodworking since 1989

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Malcolm the Boat ‘RIP’

Woodworking for me is in my blood as a son of a traditional boatbuilder. My Father Malcolm Kett was highly skilled and inventive individual often referred to as ‘Malcolm The Boat’.

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Marcus Kett and my Mortar!

Although I have spent a considerable portion of my life seeking further education and gaining qualifications in woodworking, electrical installations, bricklaying and to top it a degree in photography.

Yes, it is a medley of possible career choices but the one that I felt truly at home with was Woodworking. Woodworking has been my staple career choice that has given my family stability.

Why do I write these guides?

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Well that’s Me

We started to write these guides to help our customers. The idea was to provide the information needed to install our made to measure wooden products that we sell on this website and directly to our local customers.

We soon received feedback from people abroad and interested readers not local to us. I like to help people and I am excited that fellow woodworkers or keen DIYers found guidance in my articles. I intend to carry on writing and producing youtube videos for the purpose of providing useful content. Please share our blog with your friends and anyone that could find interest in the magic of working with wood.


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About Wallybois

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Wally is the middle one

We have lived and worked here in the Limousin Nouvelle Aquitaine since 2010, building window shutters and external doors. Our Volet manufacturing business is based at our home property as a ‘Cottage Industry’. We are a small business operating partly (60%) off the grid and try our best to practice our woodworking ethically.

How did we come up with the trading name ‘Wallybois’? Well, it is simple really, my best buddy ‘Wally’ and the fact that ‘Bois’ is French for wood and we live in France.

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By Marcus Kett, Woodworking since 1989

Based in the Nouvelle Aquitaine of France

Tel: +33 7 81 45 32 82