Friday, August 26, 2011

Belated Thursdsay: It's Technical.

(Simple) Quilter's Math 101, plus other Useful Figures to Know
All values are written using the King's System (what we use here in the States). For metric, use this converter to change what you need into Metric. Yeah, I know...Metric would make this math much cleaner.

Quilt Sizes
These are approximate. Everyone's preference for how they like a quilt to lay on a bed is different, as well as the definition of the bed size - some people calculate the "normal" overhang considering the mattress height in the equation, and others calculate for the top of the mattress only. You will find different measurements for these values all over the internet. The best thing to do, if you can help it, is calculate for the mattress you will be making your quilt for.

These measurements are for mattress top only. For overhang on sides, decide how much overhang you want (say, 10") multiply it by 2 (once for each side, so 20") and add it to the width of the bed size. Decide your overhang for the bottom, and whether you want the quilt to cover the pillows or not, and add those measurements together and add that total to the length measurement.

Crib: 23" x 46"
Twin: 39" x 75"
Double: 54" x 75"
Queen: 60" x 80"
King: 76" x 80"

Yardage Amounts
(Yardage amount as a fraction = as a decimal = length)
Decimals rounded to the nearest hundredth
Inches rounded to nearest whole inch
1/8 = 0.13 = 5"
1/4 = 0.25 = 9"
1/3 = = 0.33 = 12"
3/8" = 0.38 = 15"
1/2 = 0.50 = 18"
5/8 = 0.63 = 23"
2/3 = 0.66 = 25"
3/4 = 0.75 = 27"
7/8 = 0.88 = 32"
1 = 1.00 = 36"

To figure total inches, calculate decimal then multiply by 36.
ex.) 1.5 yards * 36 = 54"

To figure out yardage amount from inches take total number of inches, and divide by 36.
ex.) 108"/36 = 3 yards

For half-square triangles, add 7/8" (0.88") to your square size. If you are using 5" squares, and then want to toss a few half square triangles in the mix,  5" + 7/8" = 5 7/8"   (5.88")

For quarter-square triangles, add 1 1/4" to your square size. If you are using 5" squares in your quilt and need quarter-square triangles as well, 5" + 1 1/4" = 6 1/4"   (6.25")

Fat Quarters
Fat Quarters (FQs)are great little stash supplementers, but sometimes we sit there and go, well, geez, what do I do with it now? You can cut multiple of different sized squares from it, and it's easy to calculate.

First, measure your FQ. It will probably say "APPROXIMATELY" 18" x 22" on the wrapper, so it's a good idea to measure - you may find it cut rich or you may come up short, so get your measurement of length and width. Square up if needed and remeasure.

For the sake of this example, let's say your FQ is indeed 18" x 22" on the nose. Decide what kind of squares you want out of this FQ - let's say you need 4" finished squares (so that means you'll be cutting 4 1/2" squares).

18" (shortest side of the FQ) / 4 1/2" (desired finished block size plus 1/2") = 4"
From one side of your FQ, you can get (4) 4 1/2" rows.

You now have (4) 4" x 22" strips, but you need 4 1/2" squares

Length of FQ (22") / unfinished size of block (4.5")* # of strips cut from the short end of the FQ (4) = # of blocks you can get from the FQ

(22/4.5)*4 = 19.5
You can get 19 4.5" squares from an 18" x 22" FQ.

So theres the math involved...but there are also charts available online. They vary as to number because of the approximate size of FQs store to store:

(99) 2" squares
(56) 2.5" squares
(42) 3" squares
(30) 3.5" squares
(20) 4" squares
(16) 4.5" squares
(12) 5" squares
(9) 6" squares
(6) 6.5" squares

Well, that's enough math and handy charts for now. Thus far, these simple maths and charts haven't failed me! Look for more next week...on Thursday.


  1. and to think I just bought a book that has all these conversions on them, etc, because i struggle so much with the whole yardage etc. crazy system you sillies have here ;)
    I guess I should just be grateful I didn't learn to quilt over there and THEN have to learn all your stuff!

    so funny, i read: "plus other useful finger" and for a moment with my sleepmadness in residence I actually wondered whether they were rubber fingers or something else XD

  2. conversions are a pain. they tried teaching us metric and then quit, then in high school tried again and wondered why it didn't take. lol. not the teachers' fault, definitely just the federal curriculum.

    well...fingers are useful in quilting, provided you don't stitch them or rotary cut them...


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