Drafting your own block is the point at which sewing stops being a matter of following instructions and becomes a matter of understanding a shape. It is not difficult, but it does demand accurate measurements, because every line is drawn from them.
Measure properly first
A block is only as good as the numbers under it. Measure over light clothing or none, keep the tape level and snug but not tight, and take each measurement twice.
| Measurement | How to take it |
|---|---|
| Bust | Around the fullest part, tape level under the arms and across the back |
| Waist | Around the natural waist, the narrowest point, not the belt line |
| Hip | Around the fullest part, usually 20 cm below the waist |
| Shoulder | From the neck point to the shoulder bone, one side only |
| Back length | From the neck bone down to the waist line |
| Armhole depth | From the shoulder bone down to the underarm |
The three blocks
Most drafting starts with three blocks, and they can be combined. A bodice block covers the torso from shoulder to waist. A skirt block covers waist to hem. A sleeve block fits the armhole of the bodice. Draft the bodice and the skirt first, then the sleeve once the armhole is fixed.
Draw the frame
A rectangle as tall as the back length and as wide as a quarter of the bust, plus ease. Every other line is drawn inside it.
Mark the levels
Bust, waist and hip as horizontal lines. Armhole depth and shoulder slope as the two lines that shape the top.
Draw the armhole
Using a French curve, a smooth line from the shoulder point down to the underarm. This is the curve a ruler cannot draw.
Place the darts
A bust dart pointing at the bust point, and a waist dart removing the difference between the bust and the waist.
True the seams
Check that the front and back side seams are the same length, and that the shoulder lines meet. This is where most drafts go wrong.
Make a toile before you trust it
Cut the block in calico, sew it with the darts in, and put it on. A block that measures right can still sit wrong, and calico costs a fraction of good fabric.
From a block to a pattern
Once the block fits, every pattern is a modification of it. Move a dart and you have a princess seam. Add width below the waist and you have a flared skirt. Change the neckline and the armhole and you have a different top. The block stays the same; only the design lines move.
Grading, and when not to
Grading is moving a pattern from one size to another. Small moves, one or two sizes, can be made by shifting the seams and the darts. Larger moves change the balance of the pattern: the shoulder and the armhole stop agreeing, and the ease in one place no longer matches the ease in another. Past two sizes, re-drafting from measurements is usually faster and always more accurate.
Check the balance, not just the measurements
A graded pattern can measure correctly and still not fit, because grading moves the seam lines without moving the balance points. Always make a toile of a graded pattern before cutting the real fabric.
The block is a long-term investment. Draft it once, check it with a toile, correct it, and every pattern you make afterwards starts from something that already fits.
