Knit weight calculator: loop length to estimated GSM

In weaving, yarns interlace over and under one another, so the calculation rests on thread density and a crimp allowance. In knitting the yarn does not interlace — it forms loops, and what governs how much yarn enters the fabric is the length of that loop. This is why the woven formula (warp/weft set × Tex × crimp) cannot be applied to a knitted fabric; in knitting, loop length is the primary variable.

Unravel one course: take out a yarn length containing a known number of loops (say 100 wales), straighten it under light tension, measure it and divide by the loop count. On the machine side the same value can be read from the yarn run-in per course. Loop length is a production parameter set on the machine, and it is what defines the character of the fabric.

In single-face structures such as single jersey, every loop can be counted from the face, so the factor is 1. In double-face structures such as rib, interlock and ponte, half the loops are formed on the back bed, so the courses × wales you count from the face is half the true loop count and the factor is 2. Omitting the factor on a double-face structure understates the weight by roughly half.

No. This tool is for WEFT (circular) knitting, where loop length is a single value. In warp knitting — raschel, tricot — yarn is fed at a different rate from each guide bar, and what governs weight is not loop length but the run-in ratio per bar (mm fed per 480-course rack). A typical raschel fabric runs 2-4 bars, so it cannot be modelled with one loop length. For a raschel programme, confirm weight by weighing a sample.

The calculation represents the greige construction as it leaves the machine. After dyeing, finishing, compacting and heat-setting the fabric draws in and the actual weight comes out somewhat above this figure; moisture regain also enters the weighing. For sample approval, rely on the weighed result per ISO 3801.