Enlarging a pattern - a tutorial

You know how frustrating it is when the pattern you love doesn't quite go up to a big enough size? It is sometimes possible to enlarge it a bit,  though I don't recommend trying to alter a newborn pattern to fit a ten year old, or a 7 year-old pattern to a women's XL. In this post, I'll show you how to make something a size or two larger. 

First, why do I not recommend changing a pattern by several sizes? As children grow (and grow into adults) their sizes and shapes change a lot, and their growth rates vary. Young children grow upwards, but surprisingly little outwards; from puberty there are more obvious changes like breasts and hips. A baby or toddler has a waist that is often larger than his or her hips, especially after food! A 7 year-old girl may well have developed a good set of gluts; the 11 year-old boy who goes swimming may have a fine pair of shoulders.

If you buy a multi-size pattern, you will often see these differences. The pattern for a 2-year old's T shirt may be much longer than for a 1 year-old baby, whereas that for a 6-year old may not be very much longer than the 5 year-old size.

But if you have a multi-size pattern, you may notice that the larger sizes are often closer together, and sometimes, there is a similar gap between, say, 5 and 6, and 6 and 7. This is a very helpful starting point if you want to enlarge your pattern. Here's how I did it with Life Sew Savory's free Sweatshirt Tunic pattern. 

It's a great pattern, but the largest size provided is age 5. My granddaughter is pushing 6, likes loose fitting clothes anyway, and if she's to get some wear from it over the winter, I really wanted a size 7.

Let's start by saying that you don't just increase a pattern by tracing a line half an inch all round the outside (as I once saw recommended). Why? Two reasons. One is that children generally grow more in height than in circumference. If you add 2 x 1/2" to the length of the pattern pieces (i.e. top and bottom), that's only one inch. (Great maths there!) But if there are two pattern pieces, let's say a front and back bodice to cut on the fold, you will be adding 4 x 1/2" to the width if you just add the half inches to the side seams, and 8 x 1/2" if you also add 1/2" to the fold line. Either 2" or 4". Really the wrong way round. The other reason is that adding 1/2" to a convex curve will make that curve longer, whereas adding the same to a concave curve will make it shorter. Your pattern will be completely distorted.

My starting point is to look for the gaps between the sizes that are given on the pattern. On the Life Sew Savory pattern, below, you can see that the length gap between the outside of the shoulder is almost exactly the same between the 3 and 4, and the 4 and 5. So I felt reasonably safe to assume that a size 6 would probably have about the same gap. Likewise, the length gap on the inside part of the shoulder (the neckline) was also similar between these sizes. So I measured the same distance away and marked a dot from both the inside and outside, joined them up, and that gave me the basis for my new size 6 shoulder line. As you can see, I also added a size 7. You push it a bit, the more sizes you try and add in this way, but I felt pretty comfortable with this as a loose-fitting style.

You'll also see that I did similar measurements on the neckline, and then eye-balled the curves.

However, it's not just a question of measuring the gap between lines. The other thing that can help you get a pattern piece that looks the right shape, is to look at the corners and points on the pattern. With a well-drawn pattern like this, you can see that for pretty much all sizes, you can join the points from one size to another with a straight line. (See below.) On all the sizes already provided, I could join the points from size 1 to 5 with a completely straight line. So if I continued that straight line outwards, I should be able to see where the point would be on my two larger sizes. (Again, I measured the length gap between the point for 4 and 5, and marked the same distance along for 6 and for 7. And then joined up my new marked cutting lines to these points.)

And here's one of the pattern pieces with its two enlarged sizes.

This may seem a lot of effort to get a larger size, but if you've got a favourite pattern that you know works, I think it's worth it.

Of course, this is the cheat's method. As I said, it won't always be possible, and it will only work, when it does, for a size or two at most. If you want to do it properly, you may need to learn how to do pattern grading. If you'd like to know more, Melly Sews has a nice guide to the principles of pattern grading.