Pattern Grading Calculator

Use Proportional grade when you are working from measurements -- you know the bust has to go from 36 to 42 inches and want the rest of the pattern to follow sensibly. Use Size-chart grade when you are working from a size run -- you have a size 8 block and need a size 14, and want the standard ready-to-wear per-size increments applied. The difference is real: proportional grading moves the waist at 75% of the bust change, while the size-chart method moves bust, waist and hip by the same flat 1 inch per size step. Both methods fill in the same result fields, so you can switch between them and compare.

In Proportional grade these percentages (roughly 75% for waist, 100% for hip, 25% for shoulder, 15% for sleeve) reflect common industrial grading conventions -- different body measurements don't all change at the same rate as bust size increases, so a simple 1:1 scaling across every measurement would distort the fit. Treat these as a reasonable starting approximation rather than a universal standard, since actual grade rules vary by garment style and brand. Size-chart grade sidesteps the question by using flat per-size increments instead.

No -- in Proportional grade, Grade Rule and Sizes to Grade only affect Grade Steps, Sizes Apart, the armhole/neck/length grades that read off Grade Steps, and the size chart. The bust, waist, hip, shoulder, and sleeve adjustment figures are driven entirely by the difference between Target Bust and Base Size Bust, independent of how many inches you've set per grade size. Neither field is used at all in Size-chart grade, where the catalog sizes supply the step count instead.

It is the magnitude of Grade Steps: in Proportional grade, the bust difference divided by your Grade Rule (inches of bust change per size); in Size-chart grade, half the numeric difference between the two catalog sizes. Either way it estimates how many standard pattern sizes separate your base and target. A smaller Grade Rule value produces a larger Sizes Apart number for the same bust difference, since each size step represents less change. Grading direction itself shows up in Bust Adjustment's sign and in Grade Steps, which is signed, not in Sizes Apart.

Each Half Grade is simply the corresponding adjustment divided by two -- the amount added at just the side seam (or just the centre front, depending on your pattern's construction) when a grading convention splits the total circumference increase evenly between two seam edges rather than adding the entire increment to one side of the pattern piece. Bust, waist and hip each get their own, because in Proportional grade the three adjustments differ from one another. Grading Validity is a separate sanity check on the arithmetic: it compares the three absolute target measurements against floors of 24 inches bust, 18 inches waist and 26 inches hip and warns if any falls below. Those floors sit under every base input's own declared minimum, so it can only fire on a downward grade -- typically a large multi-size grade down from an already-small base, exactly the case where plausible-looking inputs quietly produce a target no adult body matches.