Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

After last week’s Bias: Definitive Essential Foolproof Guide post, today I want to go practically: how can I bias cut a rectangle, having only its measurements?

Math is closely related to sewing and I feel like a lot of self-taught sewists try to skip this part, but I think it’s a huge mistake: math is FUN – and I’m going to teach you a quick and practical trick!

Let’s talk about Pythagoras Theorem!

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

One of the features of The Sheer Plaid Top (my first pattern to be sold – actually under testing – release date February, 1st) is a softly draping collar, bias cut without a pattern piece, only having its measures…

I received so many questions about how to do that, that I realized it wasn’t as obvious as I though!!

Let’s clarify, and I hope that, when you’re finished reading this post, you’ll catch how easy is to bias cut a rectangle!

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Bias Cut – Practical Trick

As we know that bias is at 45 degrees to a fabric’s warp and weft threads, then we can use Pythagorean’s  rules about triangles!

Look at my example photo: as you can see, my meter stick (a 24″ quilter’s ruler is perfect for this task) is placed exactly along the bias (hypotenuse of our right-angle triangle isosceles), because the width (A) and the height (B) of the same triangle (where I put my two measure tapes) are the same length.

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

The fun part is that, if you know your hypotenuse length (= our bias length), you can calculate width (A) and height (B) with this easy formula:


where square root of 2 is ALWAYS 1.4142135

…wait… what?

Ok, let’s simplify for those who don’t eat bread and math for breakfast!

Our example bias piece will be 25 cm long, 3 cm height, so:

  1. Measure from your fabrics angle between crosswise direction (A) and selvedge (B) the same measurement, that is:

25/1,4142135= 17,7 cm

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras) 

  1. Fold your fabric along the bias line (you can help yourself with some pin, of a chalk line…)

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

 and cut along that fold!

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

  1. Measure desired height perpendicularly to the bias (3 cm in our example). Here too you can proficiently use your quilter ruler to trace a line 3 cm far from the bias cut.

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

and cut again!

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

  1. Finally, cut out your strip heads, just to have a rectangular (and not trapezoidal) shape:

Serger Pepper Tutorial: Bias Cut: Lifesaver, Quick & Practical Trick (feat. Pythagoras)

 That’s it!

Is that hard to do? Not really…

Hard to remember? You don’t have to, simply… just pin this post 🙂

Serger Pepper - Cut on Bias - How exciting is this math trick (feat. Pythagoras) ok

That’s all for today, stay tuned to discover what comes next… or learn how to design your own clothes… on the bias!


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About the Author:

Hi there! I love sewing, creating my own patterns and refashioning pre-loved clothes... If you love the same things, why not be friends? See you on Pinterest


  1. Beatriz Azuara January 21, 2014 at 10:17 - Reply

    I was delighted to start the morning with Pythagoras jajaja, very well explained.


    • Mamma Nene January 22, 2014 at 12:06 - Reply

      Hi Bea!
      You know, there’s nothing like Pythagoras and coffee, early in the morning LOL
      Thanks for liking my blog post – I realised that what was obvious to me, wasn’t for the others, so the post!!! I’m sure it will help more then one beginner sewist, while sewing my Sheer Plaid Top!

      • Beatriz Azuara January 22, 2014 at 12:56 - Reply

        There are things we take for granted maybe then we realize that there are many more people who do not know, sometimes it’s almost better to err with explanations and give almost all done as if for the first time you put in front of a fabric .

        • Mamma Nene January 22, 2014 at 14:05 - Reply

          You’re true, Bea!
          I sometimes feel like I’m explaining too much, but then I realze that the ones that already know them can easily skip them, but who ignore them feel lost!

          …and this is why I’ve started my Sew Basic Series: just to collect some of those little pearls so I can link up to them when I need to explain something that they often ask to me (lazy girl)

  2. Simple Nature Decor January 21, 2014 at 14:27 - Reply

    Very creative and easy to do, I love to sew and this is a great trick, thanks Maria httpt:// This friday I will be having a link party, hope you can enter another sewing DIY

    • Mamma Nene January 22, 2014 at 12:08 - Reply

      Hi Maria, thanks for liking my bias little trick 😉
      I will link up for sure, I’ve put a note on my calendar and going to follow your blog now 😉

  3. Lynet Witty January 21, 2014 at 20:05 - Reply

    thank you for this! so helpful as I only needed a tiny bit of a strip to complete my project. 🙂

    • Mamma Nene January 22, 2014 at 12:10 - Reply

      Great Lynet (I love your name!)!
      This is being with the right post at the right time in the right place LOL
      Can’t wait to see your project, let me know how did my trick worked… It’s a tiny trick but powerful indeed 😀

  4. cucicucicoo January 23, 2014 at 10:42 - Reply

    “Feat. Pythagoras”!! You are so funny, Irene! I just read both bias posts now… great stuff! 🙂 Lisa

    • Mamma Nene January 23, 2014 at 14:01 - Reply

      thanks Lisa! I tried to contact Pythagoras to ask himif it was a problem to feature him, but he still has to answer to me LOL

  5. Heather Feather February 4, 2014 at 04:54 - Reply

    Great quick tip! I’ll remember this!

    • Mamma Nene February 4, 2014 at 23:50 - Reply

      It’s really easy, I bet you’ll remember!!

  6. Pam @Threading My Way February 8, 2014 at 05:57 - Reply

    I thought my days of reading about Pythagorus were over… LOL!!! Great tip, Irene.

    • Mamma Nene February 9, 2014 at 10:35 - Reply

      Thanks Pam, for liking my little trick and featuring it too <3

  7. L. Michel February 8, 2014 at 21:28 - Reply

    Hello, found you through Threading My Way, thank goodness it is afternoon, more than 2 cups of coffee for such big words, but liked how you explained for us non bread and math people…….signed for your newsletter, love the way you make tutorials….

    • Mamma Nene February 9, 2014 at 10:46 - Reply

      Thanks L.Michel! I’m sorry for forcing you to an overload of caffeine, I hope it’s worth it!
      Serously: thanks for liking my little trick and my tutorials, I put my heart inside each one 🙂
      Welcome to our monday’s newsletter too, enjoy it <3

  8. […] She also has a great little tutorial for working with bias here […]

  9. […] Check my Pythagora’s trick about how to cut a bias piece, given its measurements here! […]

  10. […] because of their curved nature, fabric ends to be cut on bias = really prone to stretch (that on bias strips is good, not that good in necklines & co.!) while handled, sewn and […]

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