Sewing Pattern Grading Calculator (Size Up or Down)
Grade a sewing pattern between sizes — enter the base size's bust, waist and hip and a grade per size (the standard 2 in / 5 cm or a custom rule) to get a full size table, then see how to split the grade across front, back and side seams and how much to add to lengths per size.
How it works
size n measurement = base + n × grade · grade per quarter pattern piece = grade ÷ 4 · typical split per piece: ½ side seam, ¼ armhole/shoulder, ¼ neck/centre · length grade ≈ 0.5–1 cm per size
Grading is the arithmetic of turning one drafted size into a range: each size step adds a fixed grade to the body circumferences — four centimetres or an inch and a half depending on the system — and because a garment is drawn as quarter pieces cut on folds or in pairs, each piece receives a quarter of that grade, distributed between the side seam, the armhole region and the centre so the proportions stay right rather than the piece just getting wider at one edge. Lengths grow much less per size, since size scales are built around girth while height varies independently, which is why length grades are a few millimetres. The ease a designer chose for the base size is carried through unchanged, so a graded 44 fits a 44 body the way the 38 fits a 38.
Worked example
A pattern drafted in size 38 with bust 88, waist 70 and hip 96 cm graded at 4 cm per size gives size 36 = 84/66/92 and size 44 = 100/82/108 cm. Going up one size, each quarter piece grows 1 cm — 0.5 cm at the side seam, 0.25 cm through the armhole and 0.25 cm at the centre — and the bodice lengthens 0.6 cm.
Frequently asked questions
Can I just add 1 cm to every seam?
For one size and a simple shape, roughly — but widths at the neck, shoulder and armhole should grow less than the side seams, and lengths only a little, or the larger sizes end up with gaping necklines and dropped shoulders.
How far can I grade from one base?
Two sizes up or down keeps proportions convincing; beyond that industry practice re-drafts from a second base size (e.g. one base for 34–42 and another for 44–52) because bodies do not scale linearly.
Related calculators
Rules of thumb from craft, radio, climbing and broadcast practice. Verify against your own materials and equipment, and for climbing gear follow the manufacturer's data and a qualified instructor — this is not a substitute for training.