How to Check a Square for 90°

From time to time we have to test our levels and squares true so it must be a right angle. New expensive equipment is needed just a few moments of your time. 

How to check Square for 90 degrees

When we say a square is Square what we mean by that is that the square is exactly 90 degrees. 

This is actually very easy and all you need is your Square that you want to test a pencil and a surface which you can draw on.

This method is so easy there is no excuse not to check for 960 degrees on a regular basis. Being 100% sure that you square is square. This simple process can save you the expensive and demorilising project failure.

A bit like measure twice cut once this test is another way to prepare not to fail. Also check our our other blog on how to check a level for level.

Follow these bullet points to see if your square is square  also check out the video.  A simple but effective method to be certain your projects are true. Don’t be complacent and maintain your tools to keep them in serviceable condition.

  • Have square and pencil ready
  • Place square on edge of table or other surface
  • With the the squares handle pointing left
  • Draw a line on the table or other surface
  • Remove square and place on table in the opposite direction
  • the squares handle should now be pointing to the right
  • Slide the square so it meets with the line that you have drawn
  • Inspect the edge of the square with the line
  • Does the square line up perfectly with the line that you drew with a pencil
  • If it does not, in that it tapers from one end to the other your Square is out of true
  • If it does line up perfectly with your pencil line then your Square is perfectly true
  • You have completed the testing of your Square

This method for testing that your Square is at 90 degrees is a tried and tested method. I’ve been using it for years. 

Watch my idiots guide video to see how I check a square for true. Watching this video again I see I am the idiot! I don’t normall sound this nerdy.

But in this video I will show you how to check a square for square. It is very important for a square to be at right angles for it to be useful. Using a tool that has discrepency will lead to a ill fitting joint or timber that is out of true.

The woodworking square needs to be 90°.

What do I do if my woodworking Square is not true?

depending on the woodworking Square that you own that needs adjustment will depend on whether you can adjust it or whether it is destined for the rubbish bin. we could just gifted to somebody you don’t like!

Truing a woodworking Square will really depend on the type of square that you have. 

  • A combination Square
  • Engineers Square
  • Try square
  • Speed Square
  • Framing Square

How to true the Combination Square?

The combination square was invented by Laroy S Starrett. Starrett is more known for it’s hole saws these days. This is a popular option that is used by woodworkers, construction and metalworking.old-rabone-combination-square

A reasonably affordable tool that is an asset to any toolkit. But like any tool that is in poor usable condition a abused or bad tool is fake security.

A good quality square will last a lifetime like the picture of this Rabone. When choosing a new square be careful and buy something that has some weight to it. Usually this shows quality and should last. A combination square made from light cast alloy will wear in the heads slot. A good cast iron combination square is much harder and suffers less with wear in the critical area. A well made combination square will require less calibration.

Testing such a tool is easy and should be completed every so often. This process will give you reasurance that the tool is at right angles.

Checking the combination sqaure is especially important as these squares can wear.

Truing the combination square is reasonably easy. The combination square usually consists of four parts.

  • A Rule
  • Screw clamp
  • Spring 
  • Head (90° 45° or Protractor)

To true this square you can file the registry nodes in the slot of the head or buy a new one

How to true the Try Square or the Engineering Square

Truing the try square is possible but not really practical. You can true the Try Square with a fine file or a diamond sharpener. You will need to use some skills if truing your own try square. 

When you check for square smark the areas of inaccuracy. Place the square in a vice exposing just the edge and make small passes with the diamond sharpener such as a DMT. Check for square and make small adjustments as you go

The Engineering square is similar to the try square as it has no adjustment in it’s design

Speed Square adjustment

The speed square are generally cast or machined. The Speed square stays square for longer. The speed square is popular with carpenters and roofers and often sold with a framing calculation book. These speed squares are not adjustable. You cannot true a speed square. 

The Framing Square doesn’t need squaring

The framing square in often made from pressed steel and unless it is bent by misfortune. 

Why Do I Write these?

We write these articles for fun and hope you find them of interest. This topic is a large one so I will be updating this topic on a regular basis so please return to keep a check on things.


I am happy to inform you that we have included some links to related products. If you decide to purchase any product we receive a modest commission and thank you for your support.

About Us, I Suppose You Might Be Interested?

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 off the grid and try our best to practice our woodworking ethically.

Please Comment

If you have any corrections or topics you think that we should add please leave a comment.  If you think we deserve it a Share would be nice.

You can Buy a Square on for the USA or for UK visiters .  Just follow the links below.