Sewing Pattern Grading Calculator
Enter the original pattern size measurements and your target measurements to get the total grade and the amount to add or remove at each seam on each pattern piece. Nothing uploaded.
Grade amounts
| Point | Total grade | Per seam | What to do |
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Learn more: grading a sewing pattern between sizes
How the tool splits a size change
Grading spreads a change in size across the points where the pattern is sewn. The tool treats a bust, waist or hip measurement as a full circumference and splits the total change into four equal parts. It treats back length and sleeve length as a length measure and splits the change in two.
For example, a bust going from 90 cm to 98 cm is an 8 cm change, and 8 / 4 = 2 cm is added at each of 4 seam lines. A sleeve length going from 58 cm to 60 cm is a 2 cm change, and 2 / 2 = 1 cm is added at each of 2 points. A hip going from 100 cm to 110 cm is 2.5 cm at each of 4 lines. For a smaller size the same maths gives a negative number and the tool says to remove it.
The seam count, not just the total, sets how much moves at each point. That is the reason a large circumference change can still be a modest change at any one seam.
The major alteration warning
The tool shows a warning when the bust changes by more than 8 cm in either direction, which is more than 2 cm at each of the four seam lines. That cutoff is the tool's own rule of thumb and only the bust is checked. Past that point, check darts, armholes and the neckline by laying the pattern against a sample, because a straight proportional grade may stop being enough.
Why a straight grade has limits
Wikipedia's pattern grading article defines it as turning a base or sample size pattern into additional sizes using a size specification sheet or grading increments. It adds that standard rules rest on body measurements extrapolated or interpolated by one of many pattern-making systems, often chosen with the target market in mind. The tool takes your own start and target numbers and applies one even split, so it will not follow a system that grades each point by a different increment.
FAQ
Why is there a warning on large bust changes?
It appears when the bust change is above 8 cm, which the tool treats as a big alteration. Past that, a simple even grade may not keep the dart placement and armhole shape right, so make a test garment.
Should every point change by the same percentage?
The tool does not use percentages. It works from the actual numbers you enter for each point, so you can set the bust, waist and hip changes separately and get a separate split for each.
Is this how ready-to-wear grading works?
It is a simplified version. Manufacturers grade from a specification sheet with set increments, while the tool grades from your own before and after measurements, so treat the result as a starting point for the pattern.