What is pattern grading?

Pattern grading is the process of taking a pattern made in one size, the base size, and stepping it up and down to produce every other size in the run. In clothing production it is what turns one approved garment into an XS, S, M, L and XL that fit like the same garment. It is not the same as enlarging a picture. Each part of the pattern moves by its own amount, and some parts barely move at all.

Why the base size comes first

A garment is designed, sampled and fitted in one size. That size gets all the attention: the toile, the fit comments, the 3D sample, the final measurements. Grading starts from it because it is the only size anyone has checked. If the base is wrong, grading repeats the mistake in every size, a little bigger or a little smaller each time.

This is why the base-size spec in a tech pack matters more than any other chart in it. It is the point the whole run is measured from.

How grading works

A pattern maker grades by moving points on the pattern, not by scaling the whole piece. Key points, such as the shoulder tip, the underarm, the side waist and the neck point, each move a set distance in a set direction for every size step. The lines between them are then redrawn through the new points.

Some points move a lot, some a little, and some not at all. On a front bodice, centre front usually stays where it is while the side seam moves out. Neck width might change by a few millimetres per size while the bust changes by centimetres. That is why an L is not an M printed at 105 percent. If it were, the collar would grow as fast as the hem, and a pocket sized for the M would look small on the XL.

Grading can be done by hand on card, or in pattern software by entering a movement at each grade point. Either way, it starts from the same thing: a set of rules.

What a grade rule is

A grade rule is a written instruction for how one measurement changes between sizes. In a Truile tech pack it is written as a base plus a step: the measurement in the base size, and the amount it changes for each size up or down. For a shirt with M as the base, part of the sheet might read:

• Bust. Base 92 cm, step 4 cm. So S is 88 cm and L is 96 cm.
• Waist. Base 76 cm, step 4 cm.
• Centre back length. Base 64 cm, step 1 cm.
• Shoulder. Base 12 cm, step 0.5 cm.
• Sleeve opening. Base 30 cm, step 1 cm.

That is enough for a pattern maker to grade from, and enough for a quality check to measure against. Every size can be worked out from the page, and nobody has to guess where a number came from.

The step does not have to be the same across the whole run. Many labels use a larger step between the bigger sizes, for example 4 cm up to L and 5 cm from L to XL. If so, the sheet should say it size by size, rather than give one step that only holds in the middle of the run.

Grade rules, base-size patterns and graded sets

These three get mixed up in briefs and quotes, so it helps to keep them apart.

• Grade rules. The written base and step for each point of measure. They are a sheet in the tech pack.
• Base-size pattern. The pattern pieces for the one size that was sampled, as a file a pattern maker or factory can plot and cut from.
• Graded pattern set. The pattern pieces for every size in the run, already graded. This is pattern-room work, usually done by the factory or a pattern grader, from the base pattern and the grade rules.

A factory that receives grade rules and a base pattern can produce the graded set. A factory that receives a sketch and the words “please grade” will write its own rules. When you send work out, say which of the three you are sending, and which you expect back.

Where grading goes wrong

• No base size named. The factory picks one, often its own standard M, and your fit sample stops being the reference.
• Steps invented from a single sample. Someone measures the garment and adds what feels like a normal step. It may suit a different customer entirely.
• Rules with no diagram. Bust plus 4 cm, taken under the arm on one sheet and at the fullest part on another.
• One step for every point. The neck grows as fast as the hem, and the small sizes pull at the collar.
• Nothing about what stays fixed. Pocket size, collar point and button spacing often stay the same, or change only every two sizes. If that is not written, it is decided at the cutting table.
• Grading before the fit is approved. Every change to the base after grading becomes a change to every size.

I once had a size run come back where the L was right and the XS could not close at the neck. One step had been applied to every point, because the grade sheet was a single line.

What a designer needs to provide

You do not have to grade patterns yourself to get a size run made. You do need to give the factory enough to grade it your way:

• The base size, named.
• A base-size spec, with each point of measure drawn on the flat.
• The size run, from the smallest size to the largest.
• Grade rules: a base and a step for every point, and any size where the step changes.
• Base-size pattern pieces, if you have them, so the factory is not drafting the base from your measurements.

If the 3D sample was approved in the base size, the base measurements can come straight from it. That is one less place for a number to drift between the garment you approved and the one that gets graded.