Sewing Tip: Squarely Boxing those Corners

Here’s another sewing tip that I had to learn the hard way.  Boxing corners looks easy enough on paper, but when it comes to actually making those corners square, eyeballing it hasn’t been good enough for me.  So for a tote bag that you’ve made by folding a rectangle in half and sewing up the sides, give that bag some depth by boxing the corners.  And prevent those corners from being wonky by measuring carefully.

First, snip the seam open at the top and lay the side seam down the center of the bag.  Press the seam open.  Next, make sure the seam is truly centered by laying a ruler on the seam.  Place a line on the ruler directly on top of the seam line, and as many inches down as you are supposed to box the corner.  In this case, it is 3 inches (which is a very deep box as far as bags go).

boxing corners1

Make sure that the fabric on the left side of the seam (A) is exactly the same as the fabric on the left side of the seam (B).  If A does not = B, then adjust the box and measure again.

boxing corners1b

Now draw a line across the bottom of the ruler and pin fabric into place.

boxing corners 2

This is the line you will sew on.  I always double stitch this line because I’m all about sturdiness and I also backstitch at the begining and the end.

boxed corner

This is a bag with an ~1 1/2″ box.

Happy corner boxing!

79 thoughts on “Sewing Tip: Squarely Boxing those Corners

  1. Thank you! I quilt and yet I never sorted that one out. It seems such a simple concept, but sometimes you need someone to put it up there and go here! that’s how it’s done! =)

    I will take any tips you got!

  2. I made my very first make-up-a-pattern bag this weekend (a fun tote bag) and used this method – thank you! The corners look great. 🙂 (Post to come on my blog, hopefull soon!)

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  4. Thanks for the tutorial. I’m a bit confused about snipping the seam open at the top. Where and how much do I cut? My corners aren’t really wonky, but I can’t make the bottom and side seams line up exactly. I’m not sure why I can’t get it.

  5. Holy cow, you sooo just made my day! I have been trying for a week and a half now to figure out these corners, looking all over online for a tutorial on this. Thank you so much!

  6. I know I just posted and all, but I had to come back and say that I just made my first successful box corners and it’s all thanks to this blog. So one more time, a huge thank you!

  7. Your tips for boxing corners are great, best of all is the ruler. I don’t have one, off to buy one now. Thanks for your tips.

  8. Regarding your instructions on boxing corners:

    Would you mind also explaining whether you cut off the extra fabric outsi8de the area sewn? And if not, what can be done to hide or secure the flap?

    I appreciate your tips very much. I’ve just discovered your website and have learned several other tips as well (like attaching magnetic snaps). I’m into bags too, and trying to find the perfect bag, with lining, magnetic snaps and a very finished inside.

    Thanks for your help. I hope you’re respond to my question above.


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  10. Thank you for a lovely and very concise tutorial. Your pictures and directions are so good and now I feel more confident that I can make my box corners look identical.
    Thanks for helping us to be able to make sharper looking projects. You’ve made my day!

  11. Thank you for your site. The article on box corners is very helpful. I have sewn clothing but never bags. Now I am inspired to try. Because of homeschooling the boys I don’t get to sew very much but it is fun, especially when something turns out well. I saw your skirt. If you want, look at this site: I saw it in a sewing magazine and have used her T-shirt pattern for my mother with great success. The XS is still to big for me but I will keep working with it until I get it right. There is a bias skirt pattern too that I haven’t had a chance to try so I can’t tell you about it.

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  13. Thanks so much for this tutorial, it has saved me from losing my mind trying to get the corners straight on my box bag.

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  18. thanks so much for posting this. my friend and i got stuck sewing a bag and your directions were so much more helpful than the pattern we were using.

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  25. Thank you for a very, very helpful tip! It was a roll of the dice if these turned out right for me before, now I have a sure way to do it!

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  32. HI craftapple. I actually recently used your tutorial for boxing corners. I was following instructions for a tote bag and it simply said to “box corners” and showed a finished pic. And, like you, it looked very easy on paper, but when I tried to emulate it….failure. So, looked up how to do it and followed your great pics. Second try…success. Thanks!

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  41. Thank you for this great tip! I have been sewing for many many many okay since I was in the 4th grade and off and on I make bags this was so helpful. I usually find the simplest form, so I remember the next time and this is not one I have figured out. I have seen other patterns where the corner are pre cut. I was wondering if you think your steps are easier Or pre cutting the corner and then sewing? Also. If I plan for a 4 inch side am I safe to to plan 2 inches for each edge plus seam allowance? Thank you again for the info!!!

    • Hi Errin!

      Thanks for your kind words! I have also seen and used patterns where the corners are precut. I use the steps above when I’m making bags without a pattern as it is easier for me. I suspect it is just a matter of preference and that it just depends on the sewer which technique they want to use. And to answer your question, yes, the base of the triangle will be 4 inches.


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  43. Do you have a pattern and tutorial for the entire bag? I’m wanting to make a bag big enough and sturdy enough to carry a three ring notebook and a book or two. Any help/ suggestions would be appreciated. Thanks, Dawn

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