Grading Stretch Patterns

Grading is the process of creating new sizes from an existing sized block or pattern. All the blocks we've created on this website so far are size 10. Do you need to create all the other sizes one at a time or is there a faster way? There are certainly faster ways if you're using a computer. Many have grading features built in so all you need to do is click a button and all the new sizes appear before your eyes in less than a second. You do need to know what method your computer software is using to grade however!

There are two different styles of grading: incremental and proportional. Each has its benefits and disadvantages. Incremental grading is where you add a fixed measurement to each node (a specific corner or point on a line) and then essentially just join the dots (see image below).

How you arrive at that fixed amount (increment) is another question. This technique is fairly universal for non-stretch pattern making so I'll assume you have at least a basic understanding of the principle. Because non-stretch pattern techniques usually add a fixed amount of ease to a garment you are able to ignore that ease when grading and simply divide the total amount of diffence between sizes by the number of panels and there's your increment. For example, the bust increment between size 10 and 12 is 4cm divided over 4 panels (88-84cm/4) or 1cm/panel. Sound simple? Well you need to know what this value is for every node on the block and indeed each is different, but at least you only have to work it out once and you have an increment set (or grading set).

But what do you do if you have only part of block panel? Well you need to calculate how much smaller the new panel is and grade up only part of the increment. Messy isn't it? Some people will redraft each pattern for each block size so they never have to calculate increments again. They feel it's faster to redraft patterns every time than calculate every time, and often they're right. Most industry specific software know where these nodes are on your block and whether or not you're using the whole block or simply part of it. They can then do all the calculations for you and hey presto you have a set of graded patterns.

Of course you could always draft the smallest and largest pattern or block, overlay them, then mark equal spaces between them for the other sizes. Something like the lines on a weather map. It works for every type of fabric and pattern and just means drafting everything twice instead of four or five times.

Increments can work the same way for stretch patterns and indeed many people do this. It only works, however, when the amount of ease is the same between sizes. If you're mathematically alert you'll immediately realise that a percentage negative ease is not an equal increment between each size. Instead it is proportional to each size. Lets consider this for size 10 bust measurements;

Size 8: 80cm x 12% reduction = 70.4cm or 4.8% smaller than size 10
Size 10: 84cm x 12% reduction = 73.9cm
Size 12: 88cm x 12% reduction = 77.4cm or 4.8% larger than size 10
Size 14: 92cm x 12% reduction = 81.0cm or 9.6% larger than size 10

So if you start with a size 10 you have a difference in bust measurement of 4.8% per size. These calculations will come out the same no matter what negative ease you use, as long as it's a percentage and not a fixed amount (like you would have learned for non-stretch). Now keep in mind that each size category is based on a standard metric bust measurement and that all the other measurements vary depending on your market demographics. True proportional grading means you'd grade by percentage across all horizontal measurements. In other words your waist and hips, for example, would be accurate for a size 10 but appying 4.8% per size would lead to minor variations in other sizes.

But what about the vertical? The length of our one piece blocks are nape to waist plus waist to crotch plus 1/2 Gusset. If we try those based on the size 10 again we get;

Size 8: 39 + 24 + 8.5 = 71.5 or 3.1% smaller than size 10
Size 10: 39.5 + 25 + 9.25 = 73.75
Size 12: 40 + 26 + 10 = 76 or 3.1% larger than size 10
Size 14: 40.5 + 27 + 10.8 = 78.3cm or 6.2% larger than size 10

So again, if we start with a size 10, we get a difference of 3.1% per size completely irrelevant of how much ease we apply. Of course you still have to calculate every single point if you're grading by hand, but always by the same percentage. You never have to remember incremental amounts ever again. The massive advantage, however, comes if you have a CAD package. For the incremental method your computer must know where your nodes are before you can grade and this requires specialist software which is expensive. For the proportional method you can skip having to calculate the true increments, ignore that nodes even exist, and simply scale up your block or pattern a fixed percentage for horizontal and a fixed percentage for vertical. It's so easy it means any simple off the shelf CAD program can do it, cheaper, faster and just as accurate.

I create every new block or pattern as a size 10, then scale the whole piece 4.8% per size horizontally and 3.1% per size vertically. For stretchwear I use the proportion technique exclusively. This is obviously because I do all my patterns on the computer but you could equally just cut your blocks and move them in or out a fixed percentage and recurve a whole lot faster than you would if you had to calculate every increment. At the end of the day it's whatever method works for you.

The other advantage to the proportional style of grading is that you can also apply this same pair of percentages to any pattern piece, no matter how large or small. This means you really only ever need to create blocks for a size 10. You use the size 10 blocks to make your patterns and then grade those! Furthermore, if you ever want to widen your size gaps for a broader fit range you simply increase your percentage.

If I hadn't managed to convince you about the advantages of CAD software earlier, I should have by now. No more endless hours of grading ever again. Just a simple push button click each time you want fully graded set of patterns.