Math is a huge part of quilting, like it or not. I'm not particularly fond of math, but it's a necessity, especially since I rarely use a pattern.
I get emails all the time asking questions like:
"I'd like to make a twin size quilt out of charm packs. How many squares do I need?"
Or, "How many more blocks will I need to make the 9 patch quilt into a full size?"
Or, "I'd like to make your stacked coins quilt, but in a queen size. How many more charm packs and how much yardage would I need?"
These are just a few that come to mind. Well, today I'm going to walk you through these and show YOU how to do the math. :) Some of this may be pretty basic, but I think it's worth covering. I work with a calculator and a piece of paper and a pencil. No EQ for me. I'm old fashioned that way.
First off, I'd like to list some basic quilt sizes:
A nice baby size quilt is around 42" x 52".
For a square baby quilt, anywhere from 36" to 42" works well.
A crib quilt measures 45" x 60".
A nice lap size quilt is 60" x 72".
Twin size, 63" x 88".
Full size, 78" x 88".
Queen, 84" x 92"
King, 100" x 92".
If you are making a quilt for a specific bed in your house, it's best to measure the top of your mattress and add the amount of overhang you want on each side, then you will have the perfect measurements for your bed. I'd recommend this, especially if you have a very deep mattress, or if you have head and foot boards to deal with. Or bunk beds.
These are target sizes. If your block calculations don't work out quite right, just round up.
Ok, for the the first question, how many charms will I need to make a twin size quilt?
A charm square=5".
Take away 1/2" (for seam allowances) and your finished square will equal 4.5".
63" (width of quilt) divided by 4.5" (finished square)=14
88" (length of quilt) divided by 4.5" (finished square)=19.56, which would round up to 20.
So 14 x 20=280 charm squares. Your layout will be 14 blocks wide by 20 blocks long. The quilt will measure 63" x 90".
Not too bad, right?
For the 9 patch quilt:
The finished quilt measures 66" x 90" for the twin size. Each 9 patch block finishes at 6" and each sashing strip finishes at 2".
Since you want the quilt to be at least 78" wide, you will need 12 extra inches. You would need 20 extra blocks (ten for each additional column) and then add in the sashing 2" finished x 2 strips. The width of the twin quilt is 66" +12" (for the two extra columns of 9 patches) + 4" (for the two extra strips of sashing) =82", which is a bit wider than your target of 78", but close enough. Plus, it's nice to have it a bit too large than a bit too small. So the number of 9 patches needed would be 70 (from the original pattern) +20 = 90 for a full size quilt. Does that make sense?
Now, for the toughest one...a queen sized stacked coins quilt using
this tutorial.
Your target size is 84" x 92".
Coins are cut 2.5" x 5", which will finish at 2" x 4.5".
The sashing is cut at 3.5", which will finish at 3".
For the width of the quilt:
11 columns of coins x 4.5" (finished width)=49.5"
12 columns of sashing x 3" (finished width)=36".
49.5" (total coin width) + 36" (total sashing width)=85.5" wide. Perfect.
Now, for the length of the quilt...
This one will be worked backwards. You want it to be 92" long. Subtract 6", for the top and bottom sashing, which will give you 86".
86" divided by 2" (finished height of each coin) =43.
So 43 coins in each column x 11 columns= 473 coins.
473 divided by 2 (number of coins that are cut from a charm pack)=236.5, which would be rounded up to 237 charm squares required.
If there are 40 charms in a pack, you would need 6 packs of charms.
For the yardage needed for
sashing, you will need 12 strips that are cut 3.5" x 86" and 2 strips that are cut 3.5" x 85.5". For this step, I'd enter those numbers into
the handy dandy quilt calculator (someone had directed to me awhile back, thanks to whomever did so, it's so very wonderful!) which will tell me that:
for the 12 strips that measure 3.5" x 86"= 2.5 yards
for the 2 strips that measure 3.5" x 85.5"=2.375 yards
for a total of 4.88 yards, to which I would just round up to 5 yards.
Ok, any questions on how to do this? Remember to calculate with your FINISHED block size, not your CUT size, or you will have a quilt that will be much smaller than anticipated.
After all this, I feel compelled to ask, (like blogger does at the bottom of their help pages) was this article helpful to you? ;)
This one actually matches my house. Bonus! ;) I have 3 Christmas quilts in my collection now, with an idea for a 4th one that's been brewing for a long time. Hopefully I can get to it soon! 
