Chapter 39: Grading Across Sizes

Once a well-fitted pattern exists for a single size, grading is the technical process of proportionally scaling that pattern up or down to produce a consistent size range — essential for anyone producing trousers commercially, and useful background even for home sewists adjusting patterns for family members or friends of different sizes.

What Grading Does (and Does Not) Do

Grading applies a consistent set of incremental measurement differences between adjacent sizes across a pattern, based on standardized or brand-specific size charts. Critically, grading assumes that overall body proportions remain constant across sizes — it is not a substitute for the individualized shape adjustments covered in Chapter 38, which address a specific body's proportions rather than a general size progression.

Grade Rules

A "grade rule" specifies exactly how much each pattern point should move between adjacent sizes — for example, a common trouser grade might add roughly 1 cm to the waist and hip circumference and a smaller proportional increase to the thigh and hem width between each size increment, with these specific values varying by brand, target body type, and garment category.

The Limits of Standardized Grading

One of the most persistent critiques of standardized grading, discussed further in Chapter 72, is that a single grade rule — assuming one "standard" proportional relationship between waist, hip, and thigh — inevitably fits some body types within a size range better than others. Two women wearing the "same" graded size may have meaningfully different waist-to-hip ratios, meaning the graded pattern fits one more precisely than the other, even though both fall within the labeled size.

Grading in Practice

Commercial grading is typically performed using specialized software that applies grade rules automatically across a full pattern, though understanding the underlying manual principles — how each pattern point should logically move relative to the size change — remains essential for evaluating whether an automated grade has produced sensible results, particularly at the crotch curve and inseam, which do not always scale in simple linear proportion to circumference measurements.

Quick Reference: What Grading Assumes vs. What It Cannot Fix

Grading Handles	Grading Does Not Handle
Proportional size-to-size scaling	Individual shape variation (Chapter 38)
Consistent size range production	Non-standard waist-to-hip ratios
Systematic, repeatable scaling	Fit issues specific to one body

Understanding grading closes the loop on Part VII: from taking accurate individual measurements (Chapter 36), to drafting a fitted block (Chapter 37), to adjusting that block for real body variation (Chapter 38), to scaling a finished pattern across a size range (this chapter) — the complete technical foundation needed before moving into the construction techniques covered in Part VIII.

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End of Part VII.