Sizing and Grading a Pattern

Sizing and Grading a Pattern

It's heartbreaking to spend the time and money sewing up a garment, only to have it not fit properly or not fit at all! Guesswork or "winging it" usually doesn't turn out well when garment sewing! Good fit starts with good sizing and grading. 

The whole process of deciding on the basic size, grading between sizes, making basic alterations can seem very complicated and mysterious. In this blog post, I'm going to break it down and help make it make sense. 

Start with the Size Chart

To begin, all patterns have a table in their instruction booklet (and most patterns have the same table on the back of the pattern envelope) that shows how body measurements correspond to the pattern designer's sizing. These tables also tell you how much fabric you're going to need. 

This is where you start to choose your size, but it doesn't end here! 

Measure your bust, waist, hips and whatever other measurements are in the sizing table. 

Typically, when I take my bust (around the fullest part), waist and hip measurements, and compare them to those on the sizing table, I find that according to the designer, I'm a Size 12 bust, Size 14 waist, and Size 16 hip. (Your basic pear-shape, in other words.) This is not unusual, very few people are a straight "Size x" right out of the envelope!

These basic body measurements are just your starting point.

Cross-check the Finished Garment Measurements

All patterns have a certain amount of ease. Ease is the difference between your body measurements and the finished garment's measurements. Ease allows room to move, sit down, bend over, and lift your arms, all those good things you need to do while clothed.

Generally, depending on the style of the garment, there can be 2 to 4 inches of ease at the bust (to let you move and breath), between 1/2 and 1 1/2 inches of each at the waist, and 2 to 4 inches of ease at the hips (to let you sit down and bend over).

Most structured fit woven garments have about two inches of ease, in other words, the finished garment is about two inches larger than the body. 

An relaxed fit, or loose fitting woven garment might have three or four inches of ease.

And a knit or stretch fabric garment might have finished garment measurements that are the same as the body measurements or up to one inch smaller, so that it fits snug to the body. 

If the finished garment measurements are included in the pattern's instruction booklet, it's a good idea to cross-check those measurements against your body to decide how much ease you actually want in this garment. If they're not included, you can figure out the finished measurements by measuring the pattern pieces, and subtracting the seam allowance.

For example, if you think you need to cut a size 16 at the hip, look at the size 16 finished garment measurement. Wrap a measuring tape around your hip and hold it together at the finished garment measurement number.

Move the measuring tape around, pull it to the left and to the right. Is that the amount of space you want between your garment and your body? Will that be comfortable? 

If not, adjust the measuring tape to a more comfortable circumference, move it around again, then look to see what measurement is actually comfortable and what you want. Check that measurement against the size chart, and see whether you maybe need to trace a size smaller or larger at that point on your body. 

Grading between Sizes

So, I know - based on the measurements I took - that when I trace the pattern, I'll need to trace the size 12 from the shoulder to the bust, trace the size 14 at the waist and the size 16 at the hip. But where and how do I change from one size to the next as I'm tracing from the bust to the waist and then to the hips?

Switching from one size to another while tracing and cutting out your patter is called "grading". So, the question is: where and how do I "grade" between sizes? 

There's a bit of science and a bit of art to grading.

First, the science. Take a measuring tape and measure from your shoulder at the neck down to your waist, the point where you took your waist measurement. (I'll say more about where your measured waist is later.)

Now measure that same distance on the pattern piece, remembering to add in the seam allowance at the shoulder, and mark it on the pattern. Then draw a horizontal line out to the waist size line. This shows the point where your traced line should line up with the waist size you've decided on. 

Do the same thing for the widest part of your hips. How far down from your shoulder is the widest part of your hips? Mark this on the pattern too. This is the point where your traced line should correspond to the line for the hip size you've decided on. 

To connect those points, take a look at yourself in the mirror. Note where you curve and where you're straight. Are you a gentle curve outwards from bust to hip? Do you go straight down to your waist and then curve outwards to your hips? Is that curve fairly even, or is there a more sudden curve just below your waist? 

Notice in the drawing below that the bust waist and hip measurements are all the same but the curves in between are quite different!

Try to mimic the curves you see in the mirror on the pattern pieces. Take more measurements if it helps.

If you typically have trouble fitting in the waist area, try measuring 4 inches above and below your waist, then measuring the pattern piece at 4 inches above and below your waist marking (remembering to account for the seam allowance!). At what point do your body measurements correspond to the waist or the hip sizes?

As an example, I was having trouble with the hip fit on some Morgan Jeans, until I realized that while my waist was a Size 14 (and fit fine) and my hips were a size 16 (and fit fine at the hip), my high hip (four inches below my waist) was a Size 18!

So I tweaked my traced lines out to the Size 18 line just at the high hip, and then curved back to the Size 16 for the crotch and rest of the leg. Perfect!

Here's another example with a Style Arc t-shirt I'm working on now. I've traced the 14 at the shoulders and bust, curved out to the size 18 at the waist, and then gone beyond the Size 18 line to the hip and below (I wanted a looser fit on this shirt...and I can always take it in if I don't like it.) (I span the two multi-size pattern groups on Style Arc and I didn't feel like buy two patterns!) 

Once you have several points or short lines on your tracing paper corresponding to your body measurements, start connecting them with smooth lines. A straight edge or French curve can help with this. 

Trace all the way around your pattern piece, add all the markings and label it. Move on to the next pattern piece. Refer to Pattern Tracing for lots of advice on pattern tracing.

Basic Alterations

Besides grading between sizes, you may need to make another basic change to the pattern sizing.

I'll write a blog post about all the Common Bodice Alterations at a later date, but for now, let's just focus on the simplest and most common: lengthening and shortening. 

Most pattern pieces have one or more sets of two parallel lines drawn across them at specific locations. These are called the lengthen/shorten lines, and they indicate the best place to lengthen or shorten a pattern piece without changing any other dimensions of the pattern piece. 

For example, if you want to lengthen a flared dress or skirt, you could simply add length to the bottom of the skirt pieces. But this will also increase the bottom diameter of the skirt (called the sweep). If you want more sweep, that's a perfectly acceptable way to lengthen your skirt. If you don't want more sweep, you need to use the lengthen/shorten lines to lengthen your skirt. 

There are usually lengthen/shorten lines:

  • Above the waistline to adjust the torso length, and
  • Above the knee to adjust the leg or skirt length. 

For some reason, I don't remember ever seeing lengthen/shorten lines on a sleeve though. If you need to lengthen or shorten a sleeve, draw lengthen/shorten lines just above the elbow. This will keep you from changing the diameter at the sleeve hem. 

To use the lengthen/shorten lines:

First draw two parallel lines on a piece of tracing paper, separated by how much you want to lengthen or shorten your pattern piece.

Next, cut your traced pattern piece between the pattern's lengthen/shorten lines. 

If you want to lengthen your pattern piece:

  1. Tape one cut edge on one of the lines you drew on the tracing paper.
  2. To make sure your pieces align with each other correctly, extend the grainline line onto the tracing paper.
  3. Then lengthen your pattern by taping the other cut edge on the other drawn line, lining up the grainline line. 
  4. Smooth out the cut and seam lines on the edge of the pattern piece to join them up across the lengthening piece. 

If you want to shorten your pattern piece:

  1. Tape one cut edge on one of the lines you drew on the tracing paper, making sure that the pattern piece is on top of your tracing paper and the other line.
  2. Then shorten your pattern by lining the other cut edge with the other drawn line (visible through the pattern piece) being sure to line up the grainline line. 
  3. Smooth out the cut and seam lines on the edge of the pattern piece to join them up across the shortened section. 

 Once you have all your pattern pieces graded, traced, and lengthened or shortened, you're ready to cut out your fabric. 

Are you on Team Scissors, or Team Rotary Cutter? 

Some Tips 

If you've traced one size from the shoulders to the bust, remember to cut the sleeve and any neckline pieces in that size! 

When checking a finished garment measurement at your hip, be sure to sit down with the tape measure around your hips! Is it too tight? Still too loose? 

Ease that is larger than the body measurements is called positive ease. Ease that is smaller than the body measurements is called negative ease. 

When you have completed grading a side seam on the front piece for example, and you are happy with the curves you've drawn, use your graded and drawn front side seam when tracing the back side seam instead of the pattern's side seam. This way, you'll ensure that your side seams match. Line up the pattern pieces at the bottom hem rather than the arm hole (remember that the front piece will be longer because of the dart).