GSM of Knitted Fabric Calculation

How to use the calculator

1. Enter the number of knitted courses in one inch of fabric in Course Per Inch (CPI). Measure along the direction in which courses are counted, using a representative area of the fabric.
2. Enter the length of yarn in one stitch in Stitch Length (cm). Use centimeters, not millimeters or inches; for example, 2.5 mm is 0.25 cm.
3. Enter the yarn’s linear density in Tex. A yarn of 30 tex has a mass of 30 grams per 1,000 meters of yarn.
4. Read GSM (g/m²). The displayed value is rounded to two decimal places. For production or specification decisions, verify fabric weight by weighing a sample of known area.

What knitted fabric GSM means

GSM stands for grams per square meter: the mass of fabric divided by its area. It is a measure of fabric weight per unit area, not a direct measure of thickness. Two fabrics can have the same GSM but feel different because their yarns, structures, finishes, and thicknesses differ. A higher measured GSM generally means more material in each square meter.

Courses per inch describe the number of horizontal rows of stitches across an inch in the appropriate measuring direction. Stitch length describes how much yarn makes up a stitch, while tex describes the yarn’s mass per unit length. Together, stitch length and tex help estimate yarn mass per stitch. To convert that into mass per fabric area, however, you also need the number of stitches per area.

The calculator does not ask for wales per inch—the number of stitch columns per inch. Without that measurement or an equivalent measure of stitch density, its three inputs cannot uniquely determine physical GSM. In particular, the default output of 0.33 g/m² should not be interpreted as the weight of a typical knitted fabric. The calculator can reproduce its stated formula, but it cannot replace a sample-weight test.

Assumptions, limitations, and a practical check

For a simplified theoretical estimate, measure both courses per inch (CPI) and wales per inch (WPI). If stitch length is the yarn length per stitch, and tex is in grams per 1,000 meters, their unit conversions give approximately:

\[\mathrm{GSM}_{\mathrm{theoretical}}\approx0.0155\times\mathrm{CPI}\times\mathrm{WPI}\times\mathrm{SL}_{\mathrm{cm}}\times\mathrm{Tex}\]

For example, using the default CPI, stitch length, and tex together with a separately measured WPI of 30 gives approximately \(0.0155\times40\times30\times0.25\times30=139.5\ \mathrm{g/m^2}\). This is an illustration, not a corrected calculator result: the calculator has no WPI field. Actual weight may also differ because of yarn variation, knitting structure, moisture, finishing, and how the fabric was relaxed when measured.

For a direct check, cut a representative piece, measure its area in square meters, and divide its mass in grams by that area. For instance, a 0.01 m² sample weighing 1.40 g has a GSM of \(1.40/0.01=140\ \mathrm{g/m^2}\). Keep the sample flat and use a consistent conditioning and weighing method when comparing batches. If you need to check length units before recording measurements, use the Meters to Feet converter; the Metric Prefix converter can help when converting millimeters to centimeters.