Altering Patterns for a Bias Grainline

I started working on a 40’s blouse over the weekend that calls for a closure-placket on a side seam.  Since I really dislike having a zipper closure on a blouse (if I can help it), I decided to alter my pattern to be on the bias.  Using a bias construction gives the fabric a bit more stretch so I can get in and out of it easier without needing a zipper.

While I’m sure many of you already know how to construct a garment on the bias, I thought this would be the perfect opportunity to show a quick and easy way to mark the bias grainlines on your pattern pieces.


  • Ruler
  • Pen/Sharpie
  • Scrap paper

I admit, I really didn’t need to include a supply list here.  But for the sake of being a tutorial, I had to include it.  :)

Step 1: Grab a piece of scrap paper, with straight edges

My scrap paper has a little V-marking on it for some reason.  heh

Step 2: Fold paper like so

Take one edge of the paper to meet the opposite edge, creating a sharp point and fold.

This folded piece of paper has the straight-vertical grainline on the left side as well as the newly folded 45 degree grainline, or bias-grain.

Below is my pattern piece that I’m altering from the straight-grain to be on the bias.  The original grainline marking is the vertical line in the center.

My tracing wheel and scissors are on my pattern piece acting as pattern weights.  :)

Step 3: Place the piece of paper underneath (or over) your pattern piece and align the straight grainline to match the pattern piece

 Step 4: Use your ruler to mark the new, 45 degree line for the bias

My pen is pointing to the line I just made using my ruler.  I actually made two 45 degree lines, one on either side of my ruler.

Here’s a detail shot of the original grainline and the new bias grainline.

Easy right?!

My bodice pattern pieces are to be cut on the fold, so below I’ve folded my fabric just like I did with my scrap paper.  You fold your straight edge to the selvage in order to create a 45 degree bias-fold, and the pattern pieces abut on the new fold line.

I’m all bias-ed up now.

I spent most of my weekend working on muslins (and also on my knitting) but was happy to be able to cut out some of my real fabric on Sunday.  Hopefully I can finish this blouse up soon, but it also means I’ll be doing some craziness: cutting & working with chiffon for the first time.  Wish me lots of luck!


In: Sewing Tutorials

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Comments (12)

  1. Meredith September 26, 2011 — 10:17 AM

    I’d assumed that it was theoretically possible to place ‘regular’ pattern pieces on the bias-fold but I’ve never tried it and wasn’t quite sure if it would work out … thank you for posting this! I have one or two vintage blouse patterns that I’d rather make on the bias than insert a side placket, and now I think I will!

    1. Liz September 26, 2011 — 11:42 AM

      YES! I made my blouse muslin using the regular grainline and made it as fitted as I could with still getting it over my head and shoulders. Then I cut the real fabric on the bias yesterday. In the evening I basted the final bias version together and it went on just as easily. It was still snug to get over my shoulders, so I had to shimmy a bit. But it was still very wearable yet fitted; I have about 1″ of wearing ease at the waist and 2″-3″ of ease at the bust.

      There’s a few tricks with working on the bias that may be helpful before sewing it up:
      1.) Baste any lengthwise grain and let it sit overnight before sewing it up for real. This gives the fabric some time to stretch and relax fully which is important with bias cut garments.
      2.) When stitching, be sure to pull on the fabric to stretch it so your seam has some ‘give’ that mirrors the fabric.
      3.) When stitching a bias section to a straight-grain section, keep the bias section on top (and again, pull slightly when stitching). This prevents any little bumps that could be created if the bias were underneath near the feed dogs.

      I’m certain there are more tricks to working with bias garments, but if you use these three basics you should be pretty good. Make sure you try your hand at bias sewing with a cotton first, just so you can get comfortable with the stretchiness. I personally feel like a cotton-bias would be easier to learn on than say a rayon.

      Good Luck!

      1. Meredith September 27, 2011 — 3:41 PM

        Great advice, thank you! (I definitely wouldn’t have thought about the bias piece needing to stay on top, but it makes perfect sense.)

        I like to keep a few cotton bedsheets on hand for testing purposes, so I’ll be sure to use them first! Thanks again!

  2. Maxine September 26, 2011 — 11:05 AM

    Wow! great tutorial! I would never have thought of even being able to do something like that. Thanks so much x

  3. Suzie September 27, 2011 — 3:09 AM

    Brilliant – thanks so much for sharing this. This is something that I have actually been wanting to do, but was a little befuddled as to how to – now that I see it, it seems so obvious!

  4. Neeno September 27, 2012 — 8:51 PM

    Great tutorial! Can this be used for any fabric?

  5. […] a bit of bias-cut on the welts & waistband (because YAY for not having to match those parts!), Liz has a great tutorial on altering pattern pieces for a bias grainline. For the actual matching at the side seams and everywhere else, Check out Tasia’s tutorial […]

  6. I just made a long dress from a pattern I had altered for a bias cut using a 45 degree angle. After I sewed the side seams and tried it on, the dress twists on me. The side seams want to hang almost to the front and back.

    What did I do wrong?

    1. Liz May 24, 2013 — 10:03 AM

      Hi Ravenna,

      I know that you have to cut the font and back on different angles, so they should form a chevron pattern at each side seam. That way the front is opposite of the back and should prevent against this twisting. Does this make sense?

  7. Thanks Liz for your help and for reminding me of the rule I had forgotten. I cut a new back for the dress, sewed it to the front and now it hangs and fits beautifully.


  8. Venora August 8, 2013 — 7:16 PM

    Hi Liz, what do you mean by chevron? Do you mean putting the pattern in opposite directions on the fold, like in you top picture with pattern pieces.?

    1. H August 19, 2013 — 9:41 AM

      I’m not Liz, but I can answer this question. YES. Your pieces of fabric still act like wovens and not knits even when they are placed on the bias. It might help to think of the fabric threads as stripes and you want v’s or chevrons at the side seams not plain diagonals. If you are still having trouble visualizing what this means, then take a marking tool (pencil, chalk, etc.) and on the side seams on both the front & back pieces within the seam allowance, draw a few lines – each one following a thread (try doing this near a placement marking or “diamond”). When the seam is sewn (or basted), if you open up the seam allowances, you’ll have your chevrons. Ok, depending on how precise you were with the markings, your chevrons might not meet at the point, but you get the idea. Bias garments done this way won’t twist as Ravenna’s first garment did. Hope that’s helpful.

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