Working With Fractional Inches
When pattern drafting, figuring out measurements on a tape measure using fractions can be confusing if you don’t make a conscious attempt to understand how to use the markings in-between each inch.
During pattern drafting, I calculate and measure in Inches, often times I find myself using Centimeters and Inches on the same draft. My advise is to stick with one or the other as it can often lead to recording the wrong measurements (speaking from experience). Nevertheless it is occasionally essential to convert from imperial to metric units or vice versa. Please note that, when converting from imperial to metric, it is acceptable to use approximate conversions.
Today I am going to show you a very easy way to work with fractional inches when pattern drafting.
FIRST RULE: Do not use a calculator when working with inches. Why? I hear you ask. Calculators calculate in 10s of units but inches are only 8 units, which is why you end up having decimal numbers when using a calculator. When we work with inches it is easier to use fractions, this way there is no converting from decimals to inches or having to use approximations.
I noticed a recurring theme in some of my pattern drafting classes; we often had to carry out lots of adjustments when we were completing our fittings; every so often, we had a difference of 2” – 3” which is quite substantial. It was quite puzzling because the measurements were accurate, but the calculations were often wrong because students made very simple mistakes when adding or subtracting fractional inches. Some of these mistakes could be pure oversight whilst others may be due to lack of knowledge about the use of fractional inches.
Let ‘s get started.
Take a look at your ruler or tailors tape measure before you begin your pattern drafting. Each inch is split into fractions (bars); on some measuring tapes inches are split into 32 fractions, some have 16 fractions in an inch, others have 8 fractions to an inch. Have you counted yours yet, how many fractions do you have?
For the purpose of this exercise, we are going to be looking at 8 fractions to an inch.
Look at the figure below. An example of a 12″ ruler. Most tailors tapes are 60″ long.
If you look closely, you will be able to count the fractions in an inch. Simply put, each inch is divided into 8 bars and these bars represents a fraction of an inch or you can say, each inch is divided into 2 halves and each half is divided into 2 halves (quarters) and these are further divided into 2 halves and so on and so forth.
Do not be confused by the fractions ¼ ½ ¾; they are the same as 2⁄8 4⁄8 6⁄8 this is because these fractions are represented in their simplest forms, If the numerator (the top number) is divisible 2, then it is not in its simplest form, so as you can see no numerator is divisible by 2.
If you look at the bars, they have 4 different lengths.
- The longest bars represent an inch. There is only one bar with this length
- The next in length to the longest bar represents the half-way point or ½. There is only one bar with this length.
- The second and sixth bars are the quarter bars i.e ¼ and ¾
- Finally, the smallest bars represent an 8th of an inch and they are represented by odd numbers 1⁄8 3⁄8 5⁄8 7⁄8
As long as you know what each fraction represents, it is easy to subtract or add any fraction. For instance we know that ¾ is actually the 6th bar and
½ is the 4th bar.
When adding or subtracting fractions, break the bars down into the simplest form and work from there. Always be careful with your calculations.
Let me set the scene for you by starting off with an instance from one of my Pattern Drafting Basics class. We are about to draft our Bodice Front. Anya has a Bust measurement plus ease of 36½”. So to get the calculation for our front bodice, we divide 36½” by 4 because we are only drafting half of the front.
Burst measurement of 36″ + ½ ease = 36 ½”
36½” ÷ 4 = ? I have seen students recording 9½” unconsciously, they divide 36 by 4 and forget to divide ½
Let’s work this out together.
36 ÷ 4 = 9
You still have ½ left, which means that you have to divide this number by 4. If you go back to your ruler and find out what bar represents ½ you will see that it is the 4th bar, that means if you divide ½ into 4 you have 1⁄8; which means your answer is 91⁄8. Hope you got the same answer?
Some of you might say, it’s not a big deal if its 91⁄8 or 9½ but I beg to differ because 9½” x 4 = 38” which means you have tagged on an extra 1½” to your pattern. If you are making loose garments, then you definitely can get away with it, however if you are making fitted garments, the difference is a big deal.
I hope this has helped you in some way. Please leave all comments and questions in the comment box below.