Pattern Grading Calculator

Frequently Asked Questions

How does pattern grading work?

Grading scales a pattern up or down between sizes by adding fixed increments at key points - typically bust, waist and hip. A common rule is 1 in (2.5 cm) per size for sizes 6–14 and 1.5 in (3.8 cm) per size from 16 up.

Where does the extra width go on the pattern?

It is split between front and back pieces and across darts/side seams. For a 1 in per-size grade, add 1/4 in to each side seam on front and back at bust, waist and hip, then true the curves.

Do length measurements grade too?

Yes, but in smaller steps. Typical rules add 1/4 in to back length, 1/8 in to armhole depth and 1/8 to 1/4 in to sleeve length per size step, with bigger jumps for petite/tall ranges.

When should I custom-grade vs choose a single size?

If your bust, waist and hip are within one size of each other, pick the largest and adjust. If they differ by 2+ sizes, blend between sizes at the side seams using the grading increments for a much better fit.

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How This Calculator Works

Grading is how a single base pattern becomes a full size range, and how you nudge a pattern that fits everywhere but the hip into one that fits there too. Each size in a pattern range differs from the next by a fixed grade rule - an increment added at the bust, waist, and hip (commonly 1 to 2 inches of body measurement per size, distributed around the pattern). This calculator takes your base body measurements, the grade increment per size at each of the three key girths, the number of sizes you want to move, and the direction, then returns the graded body measurements at the target size. Crucially it also returns the amount each pattern-piece seam line must shift, because a pattern is cut on the flat at a quarter of the body circumference per piece edge: a 2-inch bust grade is only a half-inch added to the front pattern edge, not 2 inches. Getting that quartering right is the difference between a clean grade and a garment two sizes too big.

Formula / Method

Total change = direction sign × number of sizes, where the sign is +1 grading up and −1 grading down. New girth = base girth + total change × grade increment, applied independently at bust, waist, and hip so each can use its own grade rule. The seam-line shift per pattern piece = total girth change ÷ 4, because a typical bodice splits the body circumference into four pattern quarters (front and back, each cut on the fold or doubled), so the flat pattern edge moves only a quarter of the body change at each girth. The number of sizes must be a positive whole number up to 12, all base measurements positive, and grade increments non-negative; grading down can never drive a measurement to zero or below or the calculation is skipped. This keeps the result a real, sewable set of numbers rather than NaN or a negative pattern.

Worked Example

Base measurements bust 36, waist 28, hip 38 inches, with a 2-inch grade at every girth, grading up 2 sizes. New bust = 36 + (2×2) = 40; new waist = 28 + 4 = 32; new hip = 38 + 4 = 42 inches. On the pattern each piece edge shifts by the change ÷ 4: bust seam line moves out 4 ÷ 4 = 1.00 inch, waist 1.00, hip 1.00 inch per quarter-piece. Grade down one size with a 1.5-inch bust rule instead: new bust = 36 − 1.5 = 34.5, and the front pattern edge moves in by 1.5 ÷ 4 = 0.375 inch. Notice the pattern always moves a quarter of the body change - forgetting to quarter it is the classic reason a "one size up" grade comes out enormous.

Common Mistakes

Adding the full body grade to the pattern edge instead of a quarter of it, producing a garment two to four sizes too large.

Using one grade rule for all three girths when a pear or apple figure needs different bust, waist, and hip increments.

Grading length (back length, sleeve, rise) by the same rule as girth - vertical grades follow their own, smaller increments.

Forgetting that ease is built into the pattern; grading the body number is fine but the finished garment already includes wearing ease.

Stacking many sizes of grade in one jump; large grades distort armholes and necklines and usually need re-truing by hand.

Tips & FAQ

What grade increment should I use? If the pattern lists its size chart, subtract adjacent sizes to read its actual grade rule rather than guessing; commercial ranges are often 1–2 inches of body measurement per size. Why quarter the change? Most bodices are cut as four quarters of the body, so each flat pattern edge carries only a quarter of the total girth change - the most common grading error is skipping this. Can I grade more than two sizes? Yes, but large grades distort curves; re-true the armhole, neckline, and crotch curve after grading two or more sizes. Different bust and hip needs? Enter different grade increments per girth - that is exactly how you blend between sizes for a non-standard figure. Does this replace a muslin? No - always sew a test garment after a grade; the numbers get you close, the fitting confirms it. What about knit patterns? Knits with negative ease grade differently; reduce the increment and always test on the actual fabric's stretch.

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