A size chart states the body measurements for which each size in a sewing pattern was drafted. A sewing-pattern number is not reliably equivalent to a ready-to-wear size. The same number can also represent different measurements across pattern brands.
Body measurements and finished garment measurements
Two charts answer different questions:
- Body measurement chart: uses bust, waist, hip, or other body measurements to identify a starting size.
- Finished garment measurement chart: shows the dimensions of the sewn item at selected locations.
The difference is called ease. Positive wearing ease provides movement. A close-fitting knit may have negative ease, meaning the garment is smaller than the body and relies on stretch. Design ease creates the intended silhouette beyond basic movement needs.
Taking measurements
Use a flexible tape measure held close but not tight, and keep it level around the body. Measure over the underwear or layers intended beneath the project. Depending on the garment, high bust, full bust, natural waist, full hip, back length, or inseam may be relevant.
Current measurements matter more than a familiar store size. Bodies change, and even a different bra can alter a bust measurement.
Choosing a size
Start with the key measurement identified by the pattern company. Tops may use high or full bust depending on the sizing system; trousers and skirts rely heavily on waist and hip. Then review the finished measurements and intended fit.
If bust, waist, and hip fall in different sizes, a multi-size pattern can often be blended between lines. Blending within an existing size range is related to, but not identical with, full pattern grading beyond the supplied range.
Measurements between sizes
Falling between chart values does not automatically mean choosing the larger size. Fabric stretch, finished measurements, intended silhouette, and feasible alterations all matter. For close-fitting or complex garments, a muslin or toile in comparable fabric is the most reliable check.
After blending or altering, verify that matching seams, notches, and pattern pieces still correspond.