Sewing

Sewing grade rules, explained simply

Last verified: 2026-11-16 · 7 min read

Your pattern is a 12; your body measures like a 16. Somewhere between those two facts lies "grading" — the systematic practice of changing a pattern's dimensions from one size to another. This page explains the logic without pretending to replace the professional references: grading has real craft in it, and the point here is to make the craft legible, not to hand you a magic table.

Key takeaways

A grade rule is the difference between consecutive sizes at one measurement point (e.g. bust +1" per size, back-waist length +¼").
Differences are distributed across several pattern landmarks — side seams, darts, armhole, neck — not poured into one seam.
Width grades more than length: in the Simplicity chart, bust gains 1–2" per size while back-waist length gains about ¼".
The standard references are patternmaking textbooks — Winifred Aldrich's Metric Pattern Cutting and comparable drafting manuals; their tables are copyrighted, so we cite rather than copy.
The resize calculator computes raw per-measurement differences from a published size chart for you.

What grading is (and isn't)

Grading is not "make everything bigger". If you scale a whole pattern piece by 110%, armholes deepen, shoulders widen, and the neck drops — a different design, not a different size. Professional grading answers two questions separately: how much does each body measurement change between sizes, and where on the pattern piece does that change belong. The answers live in grade rule tables, which pattern companies derive from their fit blocks and measurement standards.

You can see the "how much" half of the logic in any published size chart. Using Simplicity's official Misses' chart (verified 2026-11-16 on their size charts page, and printed on our measurements cheat sheet), a single size step from 12 to 14 reads:

Measurement	Size 12	Size 14	Grade difference
Bust	34"	36"	+2.0"
Waist	26½"	28"	+1.5"
Hip	36"	38"	+2.0"
Back waist length	16¼"	16½"	+0.25"

That asymmetry — two inches at the bust, a quarter inch of vertical length — is the entire philosophical content of grading. Bodies change circumferentially far more than they change longitudinally, and grade rules encode that.

Where the difference goes: distribution

The "+2" at the bust never gets added in one place. On a basic bodice front, a typical distribution walks the pattern outline: a slice at each side seam, a deeper or longer bust dart, a touch at the armhole, perhaps a whisper at the shoulder. The exact split is the patternmaker's judgement and depends on the block, the silhouette, and the company's fit philosophy — this is the part the textbooks teach and why we point you to them rather than inventing rules.

What we can state honestly is the arithmetic floor: if the total bust grade is +2" and you are using the two side seams as your only grading points, each seam moves out by ½" (the garment's full circumference gains 2" across front and back pieces, 1" per piece, ½" per seam). Adding more points (darts, armholes) shrinks what each point must carry. The grade calculator's custom mode does exactly this split for any measurement and any number of points you name.

References worth owning (and why we don't copy their tables)

The standard sources for full grade rule tables are professional patternmaking texts. The one most often cited for metric drafting and grading method is Winifred Aldrich, Metric Pattern Cutting (in its women's wear, menswear and children's wear volumes; later editions carry updated size charts and grading sections). Comparable standing goes to the major fashion-school drafting manuals, such as Helen Joseph-Armstrong's Patternmaking for Fashion Design. These books cost less than two ruined garment cuts and answer "exactly how many millimetres at which landmark" for blocks they draft themselves. Their tables are copyrighted work — we cite the authorities and recommend the books, but the tables on CraftCalc come from publicly published size charts (Simplicity's, the Craft Yarn Council's) with links, never from the textbooks.

A worked grade, start to finish

Scenario: a fitted bodice in size 12 must become approximately a size 16 (four sizes up; two full grade steps of two sizes each in this chart). From the published chart, size 12 → 16 totals: bust +4", waist +3½", hip +4", back-waist +½". Doing it in two steps of two sizes each keeps intermediate landmarks sane and lets you stop at 14 if a muslin says so. Walk each step: slash or shift the pattern at your chosen points (side seams, darts, armhole), add the step's share at each, then true the lines — check that the armhole curve still meets the sleeve, that the dart legs stayed equal, that the seam lengths still match front to back.

The verification half of grading is unglamorous and essential: measure the graded pattern's seam lengths against its partners (front side seam vs back side seam), and compare finished measurements against the size chart's target — the chart on the body measurement tables page. If grading is arithmetic plus judgement, the muslin is the exam.

Grading versus the easier alternatives

Before grading by hand, check the obvious: most major-brand patterns come in multiple nested sizes, and cutting a blend (size 16 bust, size 12 shoulder, graded smoothly between) is often 90% of what a custom grade achieves. Length changes — hem, waist placement, sleeve — are edits, not grades. And knitters have it easier still: a knitting pattern's "sizes" are pre-graded circumferences, so resizing is closer to picking the nearest size and adjusting lengths, per the resizing guide.