Thursday, September 12, 2013

Handy Sewing Math Chart

While pattern drafting Little Miss' Cream Puff Dress (stay tuned for more on this), I realized that some measurements are difficult to convert to sewing measurements.  I thought it would be handy to create a chart for quick reference.

What, you mean sewing involves math?


How to Use This Sewing Math Chart

When calculating measurements for pattern drafting, you will encounter some odd {I mean, weird} numbers.  For example, you take a measurement that needs to be divided by 5; you get a measurement of 37 and 5/8.  What do you do?  There are different ways to solve this problem, all of which involve either math in your head, or math on paper.  Neither of which makes me feel very confident of my results.

1.  In this case, your fraction is already divisible by 5, so you only need to divide the 37 and then add the 1/8.  What do you get?  37/5 = 7.4  But now you have to figure out how to add 0.4 and 1/8.  Arrgh!  This is when I start getting frustrated.  What I want to show you is how to get the most accurate measurement for pattern drafting.  So I will walk you through the calculation in three different ways.  *Note:  my chart rounds up to the nearest 1/100.  Generally, you will also want to round up to avoid any pattern piece being too small.  The examples below will demonstrate why.*

2.  Method A:  Estimate, doing math in your head.  We need to add 0.4 and 1/8.  0.4 is almost 0.5, so you could add 4/8 and 1/8 and get 5/8.  So now your pattern piece would measure 7 and 5/8.  Sounds easy, right?  To check our math, let's now multiply our result by 5; we get 38.15.  This means the total circumference at that point on the body will be just over 38 inches.  We wanted it to be 37 and 5/8.  The result will be almost half an inch too big, just because we rounded up by 0.1 before using this measurement.  So, while this is the easiest method, it could lead to more frustration in the fitting stage of sewing.

3.  Method B:  Estimate, knowing that 1/16 = 0.06.  So, we need to divide 37 and 5/8 by 5.  We could convert 5/8 to 10/16, which equals 0.6.  37.6 divided by 5 = 7.52.  Now, checking our math, 7.52 x 5 = 37.6. This result is very close to 37 and 5/8.  (5/8 = 0.63)  This method works well, as long as you want a close fit, or if there is enough ease built into the measurement so that it won't matter.  But any tiny little deviation of your stitch from the exact sewing line could make a garment that is just slightly too tight.  That's much worse than too big.  Too big can be pinched out at the seams, but too tight means starting over.  Plus, the mental math is more complicated than in Method A.  I'd rather use Method A, and have a simpler fitting session.

But you might wonder, why is it so close, but just a bit on the smaller size?  This is because 1/16 is really 0.0625. So 1/8 is just a bit more than 0.06 + 0.06, it is actually 0.125.  The more times you multiply by a factor of 0.06 as an estimate for 1/16, your estimated measurement is coming out just that much smaller.

4.  Method C:  Use my Handy Sewing Chart.  Since I've already rounded to the nearest hundredth, the factor of error does not increase as your fractions increase in multiples.  (Does that make sense?  Sometimes, for me, numbers and words are incompatible, so even though I know what I mean, I can't explain it accurately.)

So let's try my example using my Handy Sewing Chart.

37 and 5/8 equals 37.63.  37.63 divided by 5 equals 7.53.  7.53 equals 7 and 9/16 on your graded ruler.  Let's do the math in reverse to double check the results.  Literally, (or, maybe I should say, mathematically?) 7 and 9/16 equals 7.5625.  Multiply this by 5, and you get 37.81.  This is smaller than Method A, and bigger than Method B, which means it is just right!  It will be 3/16 larger than the measurement you took--37 and 5/8.  This is practically negligible, which means your garment will fit perfectly. 

In my view, for a fitted garment, you have enough room to breathe, but not so much that your strapless top will need to be pulled up constantly.  No fidgeting required! 

For a garment with ease already included in the pattern, this means a perfect fit.

Till next time,--Ayana

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