How to use the humble L-square or tailor’s ruler

Nearly everyone has an L-Square made by Fairgate, sometimes called a tailor’s square or rule for pattern drafting; these are indispensable. Today I’d planned to tell you all about the various uses of them but time has a way of catching up with me. Instead, I’ll tell you about them in the context in which the subject came up. Below is a drawing of one. The typical square is 14″ X 24″ making them difficult to photograph. A larger view is here.

The question was:

I was wondering what is the best way to make half scale patterns. Should I only draft half of every measurement when doing a basic block? If I have a measurement of 14″ the ruler will break it down to 7″?

The answer is yes. The ruler has a built in math cheat sheet. Below are some of the scales marked off. The ruler also breaks down into 6ths and 12ths on the long arm and 8ths and 16ths on the short arm. See below if not from here.

To easily draw only half of 14, you draw from the zero point, up to the 14 on the halves portion of the scale. This will equal 7″ as shown below.

See, it’s very simple to cheat on figuring measures with your L-square.

Now maybe when I have more time, I can explain how this tool is used with archaic pattern books to draft patterns. For example, if you’ve ever read the texts of these older books (meaning before 1960), you’ll see frequent directions to draw a line that is 1/6th of breast or something similar. This would mean to draw a length from zero up the number on the scale of 6ths that represents your chest. Nifty, huh?

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  1. Gidget says:

    Another Duh moment. I went to the trouble a making and printing a lovely table of aliquot parts – color coded even – and it was on my ruler all along!!! Thanks for more great information.

  2. Sandra B says:

    I’m making a bunch of half-scale patterns as a teaching aid for my students, so I copied my tape measures and rulers at 50% on my scanner/printer. I wasn’t expecting them to turn out as accurately as they did. I then used a glue stick to attach the paper to firm recycled plastic packaging (from a toy – a doll who claims she loves the environment, but weighs 180g while the packaging weighs 235g. Grrr). I do have a tailors square – and know how to use it – but it’s too unwieldy for my small desk at home, where I do most of my prep work after the evening chores. And I wanted a flexible half-scale tape measure to go with the half-scale dummies I’ve made, so I covered one of the lengths of paper in clear contact paper. I can now draft exactly to the measurements and end up with a half scale pattern and no maths. I like to reduce the operations to the minimum to reduce opportunities for error. Well, that’s what I tell the students. I’m really just lazy about maths.

  3. Terri Dans says:

    Nice to see the tool I use every day!
    I don’t know how many people use a square anymore or know about the old style drafting methods, but I do. It’s so much easier than trying to use a table of aliquot parts. If you are familiar with the old drafts, you will see that a book like Metric Pattern Cutting for Menswear has unfortunately discarded the tailor’s square as a tool, but the drafting formulas are mostly still based on the divisions of the square, like the older drafts it is derived from.
    I think that you can buy a 1/2 scale square too, so you can just use it as you would a full size one, but the numbers still coincide to half chest or waist or whatever body measurement that you are using the square for.
    I don’t know if patternmaking courses still use it? Do you?

  4. Rebekah says:

    Did you ever write up instructions on how to use an L-square to draft patterns from the “archaic pattern books”?

    I have several old tailor methods downloaded from, along with copies of LOADS of the old drafts found in Godey’s, Peterson’s and the likes.

    I sure would love to have some guidance in modern language!!!

    If you’ve not written anything yourself, perhaps you know of a comprehensive guide elsewhere on the www?

    Thanks :)


  5. Betty says:

    Can someone please tell me if the same principle applies if you want to measure a 1/3rd or a 16th, 4th and so on? Thank you in advance.

  6. Kathleen says:

    I’d mentioned as much in another post, don’t know which now but probably one related to draping on half scale forms.

    There is a trade off. Only certain weights will behave reasonably well in half scale. Georgette is one that comes to mind.

  7. Marlece L White says:

    Is there a publication the demonstrates all the increments and haves, and thirds and miters on the Tailor’s L-square?

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