How size grading works: from one sample to a size range

Size grading is how a brand gets from one garment to a size range. A pattern is made and fitted in one sample size, and once the fit is approved, every point of it (chest, waist, hips, length, sleeve, neck) is moved out or in by a set amount for each size up or down. That amount is the grade rule, and the set of rules is what makes your M an M and your XL an XL.

Your size chart is that grading, made visible. Read it across, size by size, and the differences between neighbors are the brand's grade steps.

From one sample to a full range

1. A sample size is drafted and fitted, usually a size near the middle of the range, on a fit model or a form.
2. Grade rules are set for each point of measure: how much the chest grows per size, the waist, the hip, the length, the sleeve.
3. The pattern is graded into every size by those rules, by hand or in pattern software.
4. A spec sheet records the result: the target measurement of each point in each size, with the tolerance a finished piece may be off by.
5. Production pieces are checked against the spec sheet, and the published size chart comes from it (or from measuring the pieces).

When only the sample is fitted, every other size is arithmetic, and the ends of the range are the furthest from what anyone tried on.

What grade steps look like

Here are the steps between neighboring sizes in Ruban Size's templates, measured from the middle of one size's range to the middle of the next:

Every number is a choice. Another brand can step its tops by 4 cm or by 6, and both are right for their own patterns.

Three patterns in real grading

Even steps

The men's T-shirts template grows 8 cm at the chest from every size to the next, S to XXL. Numbered sizes step evenly when the number is the measurement: the women's jeans template labels each size by its waist in inches, so each size is 1 in more, and men's pants step 2 in at a time.

Steps that widen

The women's tops template starts at 5 cm and ends at 7.5 cm per size. Its ranges widen too: the XS covers a 4 cm span of chests (80 to 84 cm), the XL a 7 cm span (103 to 110 cm). The larger sizes cover a wider spread of bodies, and the steps between them widen with them. The Girls' dresses template does the same at the chest, from 2 cm between sizes 4 and 5 to 5 cm between 12 and 14.

Where a step changes is called a grade break. One step for the whole range keeps the chart simple; changing the step lets the ends of the range follow the bodies they are made for, at the cost of a chart that looks less regular.

Lengths grade less than girths

In the women's tops template, the chest grows 5 to 7.5 cm per size while the length grows 2 cm and the sleeve 1 cm. Lengths follow height and girths follow build, and the two don't move together.

Some lengths stop growing altogether. The men's pants template keeps a 32 in inseam for every waist, the women's jeans template changes it once (30 in up to size 29, 31 in from size 30), and the scrubs template's regular inseam stops at 81 cm for 2XL and 3XL. Height is handled by separate lines instead: the scrubs template's tall inseam is 8 cm longer at every size, and the petite template keeps the same girths as the regular dresses while cutting the lengths shorter (petite and tall are lines of their own, graded for length).

Why grading matters for your size chart

Check the steps when you measure. Measure every size of a style at the same points and write the differences down. They should be steady or widen smoothly. A dip or a jump means a piece was measured wrongly, or graded wrongly. How to measure a garment flat covers the points.

Don't copy another brand's grading. Their steps describe their patterns. Paste their numbers over your garments and your M carries their M (why a medium isn't the same size everywhere).

Keep tolerances under half a step. If a finished piece can be off by more than half the grade step, two neighboring sizes can measure the same. Tolerance in size charts works through the numbers.

How Ruban Size reads your grading

Find my size uses the steps of your chart directly.

• Ranges with no gaps. A chart that says 80-84 then 85-89 leaves a centimeter between sizes. Find my size splits it halfway, at 84.5 cm, so every measurement belongs to a size.
• Distances in size steps. The step of a measurement is the middle value of its center-to-center differences. A shopper half a step past a range counts as a near miss, one two steps past as far off, whatever a step measures in centimeters. Too tight costs more than too loose on the measurements that matter, as in "go by your largest measurement".
• Values must grow. A measurement that doesn't grow with the size can't be read as ranges. A length that is the same for every size, like the men's pants inseam, gets a line that says "the same for every size" and doesn't move the answer. Sizes that share a value, like the jeans inseam, share one range.
• The fit scale moves by a share of a step. "Runs slightly small" moves the shopper's target up by a fifth of a step, "Runs small" by 0.55 of a step. So the same setting means the same thing on a chart that steps 2 cm and one that steps 8.

Try it on the women's tops chart, whose steps widen from XS to XL:

To build your own, paste your spec sheet into the size chart editor or start from a template like Men's T-shirts, with body and garment measurements in two tabs, and replace the values with yours. The size grading entry of the glossary sums up the terms.

Questions

What is size grading in clothing?

It is the process of scaling one approved sample pattern into every size of a range, moving each point of the pattern by a set amount per size. The amounts are the grade rules.

How much does each size go up?

It depends on the brand and the garment. In Ruban Size's templates, women's tops grow 5 to 7.5 cm at the chest per size, men's T-shirts 8 cm, shirt collars 2 cm, and lengths 1 to 2 cm.

Why do larger sizes jump more?

Larger sizes often cover a wider spread of bodies, so the step widens with them, as in Ruban Size's women's tops template (5 cm at the small end, 7.5 cm at the large one). A single step for the whole range is simpler.

What is a grade rule?

The amount one point of a pattern moves from one size to the next, such as 2 cm at the collar or 1 in at the waist. A garment has one rule per point of measure.