Fabric formula

Knit GSM from loop length formula

Estimates single jersey weight from courses and wales per inch, stitch length and yarn count.

Formula

\text{GSM} \approx \dfrac{\text{CPI} \times \text{WPI} \times 1550 \times \ell \times T}{10^{6}}

Symbol	Meaning	Unit
CPI	Courses per inch	per in
WPI	Wales per inch	per in
ℓ	Stitch (loop) length	mm
T	Yarn count	tex
1550	Square inches per square meter	in²/m²

When to use it

Use it to understand how stitch length and relaxation drive knit weight, or to cross-check a lab GSM against the knitting settings.

Worked example#

Relaxed single jersey: 50 CPI, 36 WPI, stitch length 2.8 mm, 30s Ne cotton (19.68 tex).

Loops per m² = 50 × 36 × 1550 = 2,790,000
Yarn per m² = 2,790,000 × 2.8 / 1000 = 7,812 m
GSM = 7,812 × 19.68 / 1000 = 153.8 g/m² (about 154)

The method assumes one loop per course per wale, which fits single jersey. Rib and interlock have loops on two needle beds and need the measured method.

Where this formula is explained

Fabric & YarnGuide3 min read

Single Jersey Fabric: Structure, Properties and Common Problems

Single jersey is the basic weft-knit fabric behind most T-shirts. How it is made, the settings that control its weight and shrinkage, its typical problems (curling, spirality, laddering) and how to specify it.

Fabric & YarnGuide7 min read

Fabric GSM: Meaning, Formula, Measurement and Calculator

GSM is the weight of one square meter of fabric in grams. Learn how to measure it with a round cutter, calculate it from any sample size, estimate it from construction, and control it in production.