Sunday, 7 October 2012

Quilt Math Part I - calculating binding

So let's start the Quilt Math series.  Calculating binding.  How much fabric do you need to bind your quilt?  Before we get started, here's a button for your blogposts or sidebar. 

Lily's Quilts Math
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I make binding from WOF strips (i.e. cut from one selvedge to the other).  I make straight binding, not  bias binding.  I usually make 2 1/2" double fold binding but we can also calculate for narrower binding.  And the fabric I am using is usually 44" wide.  So this tutorial is based on 2 1/2" double fold WOF binding from 44" fabric.

1.   How long does the binding need to be?  The binding needs to be as long as the outside perimeter of your quilt plus a little bit for corners (see step 2).  So, if we have a quilt that is 70" x 90", we calculate 2 x 70" = 140".  Then 2 x 90" = 180".  Then add those two together.  So 140" + 180" = 320".  So we've added up the outside edges of the quilt.

2.   Then add 1" per corner since mitring corners does take a little bit of extra fabric.   So add on 4".  320" + 4" = 324".

3.   If you're using fabric that is 44" wide, I take off 2" to account for selvedges and pre-washing shrinkage.  I then take off an additional 4" to deal with the fact that, when making a diagonal join on a length of binding, some fabric is lost in those seams.  So we are making calculations with fabric that is 38" wide.

4.   To work out how many 38 WOF strips needed to make 324" of binding, you need to divide 324" by 38".  So 324"÷ 38" = 8.53.  Round 8.53 up to 9.  Always round up, never down or you will end up with less than you need.  So we need 9 WOF strips.

5.   If cutting 2 1/2" binding, you need to multiply the number of WOF strips (9) by the width of the binding (2 1/2" or 2.5").  So, 9 x 2.5" = 22.5".  So for a quilt 70" x 90", you need 22.5" of fabric.

6.   Since a yard is 36":

  • 1/4yd is 9"
  • 1/2yd is 18"
  • 3/4yd is 27"
  • 1 yd is 36"

So you will need 3/4 yd fabric for this binding.

7.   Since a metre is roughly 39 1/2":

  • 1/4 metre is roughly 9 3/4"
  • 1/2 metre is roughly 19 1/2"
  • 3/4 metre is roughly 29 1/2"
  • 1 metre is roughly 39 1/2"
So you will need 3/4 metre fabric for this binding.  


8.   So here is a shortened version of how you calculate your binding requirements:
  • Calculate 2 x width.  
  • Then calculate 2 x length.  
  • Add those two together and add on 4" for corners.  
  • Divide the whole lot by 38" (the width of 44" wide fabric after taking out selvedges and diagonal seams). 
  • Multiply that figure by 2.5 for a 2 1/2" binding.
  • OR multiply that figure by 2.25 for a 2 1/4" binding.
  • OR multiply that figure by 2 for a 2" binding. 
9.   Or in algebra, where W = width and L = length:

2.5 x ((2W + 2L + 4) ÷38)   = the amount of fabric required to make a 2 1/2" double fold binding.
2.25 x ((2W + 2L + 4) ÷38) = the amount of fabric required to make a 2 1/4" double fold binding.
2 x  ((2W + 2L + 4) ÷38)     = the amount of fabric required to make a 2" double fold binding.

Your homework is as follows.  Calculate how much fabric is required to bind the following quilts with a 2 1/2" double fold binding cut from 44" fabric.  Answers at the bottom of the post in case you want to double check your calculations!

A.   50" x 50" quilt.
B.   60" x 80" quilt.
C.   40" x 40" quilt.

At the risk of sounding a wee bit of a #quiltmathnerd, I'd love to hear how you calculate binding.  And please comment or email if you're struggling with any of the posts in this series.  I know quilt math doesn't click with everyone so please let me know if you can't quite wrap your head around it yet.

Answers:

A.   15"
B.   20"
C.   12.5"

35 comments:

  1. Thanks for this great tutorial, look forward to the rest of the series, I will link up a post and share on my facebook page as it is brilliant!

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  2. I do it your way without taking out selvage allowance. I have never been caught short, so to speak, but will take it into account from now on. Great tutorial Lynne. Di x

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  3. I calculate binding by going to this website http://quiltbug.com/articles/binding-calculator.htm and checking their chart!! :o)

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  4. Lynne, your method is great but I guess I have leaned to cheat. I have a free app on my iPad called The Quilter's Little Helper by Robert Kaufman fabrics...all I have to do is fill in a few boxes with WOF and width of binding and it spits out the number of strips I have to cut. But if my battery is charging, I will use your method! Thanks for sharing!

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  5. Thanks so much for doing this series Lynne. I will be referring back to this post next time I do binding. You may need to sit down if I tell you how I do it now? - I grab some fabric and cut it up until it looks about right. Then two things happen - either I find I'm short by about 6" and have to hastily try adding an extra strip whilst the rest is attached to the quilt or I end up making so much I have enough to wrap round my house about twice. I'm not joking about any of this. Sometimes patterns tell me how much to make. But I'm sure I don't do anything fancy like try and work it out for myself with proper maths and stuff.

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  6. Very nice binding post. I use this method...sort of. I measure the side of the quilt and then sort of guesstimate how much I need. I always add a bit extra so I don't run short. If I actually do the math (sometimes) I have less leftover at the end.

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  7. We think alike. This is exactly how I do the math. Being an accountant is handy at times.

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  8. I do basically what you do, but I skip the step of adding extra for the corners and all of that. If I come up with 8.124 or something similar I know that 9 strips will cover all of that anyway, if I come up with 8.983 I just do 10.

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  9. Great tutorial! I pretty much do the same but my general rule of thumb is just 2 x the sides + 2 x the length + 15 inches. Don't ask me why 15 inches but it just always seems to work. Your way is much more thought out :)

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  10. I like that you have set out nice algebra statements, very mathnerdy! I add 10" not 4" for corners and such but there is always extra, otherwise this is exactly how I do the calculations too.

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  11. I use a similar method, although I didn't think to use 38 inches instead of WOF. I used the actual WOF, then added an extra strip to cover contingencies. Your method is more exact!

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  12. I also use a similar method but add an additional 12" and have never been caught short, however this is great having the guess work taken out of just how much fabric to purchase when needed! Thank you very much for all the time you are putting into the mathematics for us. :)

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  13. I calculate the perimeter, add 12", divide by 40", and add an extra strip just in case.

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  14. I do it just like you do, and I was a math major. Your instructions were clear as day. Thanks.

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  15. Wonderfully clear instructions! I do it just like you but instead of working with a 38" width I assume 40" (but then add 20" to account for corners and the diagonal joins) because 40 is an easier number to work with. (I try not to use a calculator...) I make my binding 2 5/8" wide as I found that I was often struggling to pull the back over the stitches (from attaching it to the front) and that extra eighth of an inch makes a big difference - I guess my 1/4" is more generous when attaching binding than it is for piecing!!

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  16. I calculate binding pretty much the same way, but I am less careful. I don't add 4" for corners, and I figure I get 40" for WOF (but I don't prewash so no shrinkage). Oh, and if I need like 5.25 WOF strips, I will often just cut 5 and then use a scrap of something else. Because I like a scrappy binding. I like to make that scrappy section fall on a corner if possible.

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  17. I do it about the same way...only using 42" as wof and adding 12" to the perimeter rather than subtracting for all of the seams etc.

    Well done.

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  18. I do it just like Cindy Sharp, above, and have never run short. ' looking forward to your future posts. I have a friend who wants to learn to quilt and plan to refer her to your blog as a resourse!

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  19. Wonderful, but my head hurt... I will print this off and keep it for reference!!! Thanks x

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  20. Thank you for this well drawn out post on the math of binding! It will be so helpful in my future projects!

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  21. Thanks for the great start to the math series! I'm happy to see that I have been doing it pretty much like you!

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  22. Oh just like the Sunday nights of olde - flashback 1984!
    I work it out the same, just hadn't thought of it as maths x

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  23. Haha, I make scrappy binding and add a bit in at the end if I haven't made enough #lazymathquilter!

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  24. I use bias binding, so I usually use the charts at jaybird quilts.

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  25. Great tute. I do it basically the same, I add 12 for wiggle room and divide by 40, never short.

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  26. Lynne,

    Thank you so much! It is clear and concise. Have a great day.

    Linda

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  27. I actually made a Quilt Binding Calculator with the help of my husband two years ago! I think this will help mathematically challenged people out there. http://www.wambers-whimsies.com/quiltbindingcalc.php

    I have instructions to calculate for double fold binding.. http://www.wambers-whimsies.com/useful-tools/

    (Didn't mean to steal your thunder Lynne!)

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  28. I forgot to add that my calculator adds 12 inches and rounds up to the nearest whole strip, so you'll almost always end up with more than enough binding to complete your quilt.

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  29. Thank you for all the work you have done to provide us with absolutely clear end precise instructions! I keep it as a valuable reference document.
    Until now I did some calculating and some guessing and I always ended up with too much binding ,so I appreciate this method that helps me to reduce my scraps!

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  30. I pretty much do the same thing when I calculate binding, but I add on about 12 extra inches so I have plenty of fabric to work with when I go to sew the two ends together. I hate wrestling with a quilt that only has an itty bitty bit of binding left to sew together.

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  31. I pretty much do the same when I'm in #quiltmathnerd mood, but nearly always I do it the way my mother measured things:

    If you are right handed:

    Hold quilt corner between thumb and fingers of right hand and stretch your arm out.

    Put fingers and thumb of left hand gripping further along length of quilt on tip of nose and measure in multiples of nose to outstretched finger grip! Remember to Count.

    Replicate that length with string or ready prepped binding. Add on a bit for fat thumbs ... then add on about half width of quilt. (if I'm doing that nifty leaving long ends for diagonal joining lark)

    Tada!

    Works perfectly for me every time. I know it's not very scientific, but it would work on a desert island with no ruler!

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  32. Thank you for your quilt math. I'm just starting quilting and a new blog and I get very inspired by yours.

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