Choosing a Jersey Weight for T-Shirts, Leggings and Sweatshirts
Knit fabrics are where fabric weight matters most to how a garment feels, and where listings are least consistent about describing it. One shop says "180 GSM jersey", another "5.3 oz", another "medium weight", and a fourth says nothing at all. This guide explains what weight tells you about a knit, gives rough weight ranges for common garments, converts them with the site's Fabric Weight Converter, and covers two knit-specific issues: how much a knit garment's fabric weighs, using the Fabric Weight from Dimensions tool, and how knits shrink in length while growing in width, using the Fabric Shrinkage Calculator.
Knit structures you will see
- Single jersey: the classic T-shirt fabric. Smooth on the face, loops on the back, edges that curl. Stretches more across than along.
- Interlock: a double knit that looks smooth on both sides. Thicker and more stable than single jersey of similar yarn, and does not curl.
- Rib: alternating columns of face and back loops. Very stretchy across the width; used for cuffs, neckbands and fitted tops.
- French terry: smooth face, small loops on the back. Sweatshirts and loungewear.
- Fleece (brushed back): like French terry with the loops brushed into a soft pile. Warmer and heavier.
- Stretch jersey and activewear knits: often polyester or nylon with elastane, for leggings and sportswear.
Structure changes how weight feels. An interlock at 200 GSM feels more substantial than a single jersey at 200 GSM, because the double knit is thicker and denser.
Rough weight ranges by garment
These ranges are a loose guide; brands and mills vary, and fibre content shifts the feel. Ounce figures are the converter's exact conversions.
| Garment | Typical GSM | oz/yd² |
|---|---|---|
| Lightweight or summer T-shirt | about 140 | 4.13 |
| Everyday T-shirt | 160 to 180 | 4.72 to 5.31 |
| Heavyweight T-shirt | 200 to 240 | 5.9 to 7.08 |
| Leggings and activewear | 200 to 280 | 5.9 to 8.26 |
| Sweatshirts and hoodies | 280 to 320 and up | 8.26 to 9.44 and up |
The converter puts 140 to 180 GSM in its Light band and 200 to 320 in Medium. For knits, those labels describe the weight, not the warmth: a brushed fleece at 300 GSM is far warmer than a 300 GSM woven twill because of the air trapped in its pile.
What weight changes in a knit
- Opacity. Light jerseys, especially in pale colours, can be see-through. Leggings in particular need enough weight and density not to become sheer when stretched over the body.
- Drape and cling. Light jerseys drape and cling; heavy ones hold their shape and hang away from the body.
- Warmth. Heavier knits, and brushed or terry backs, are warmer.
- Durability. Heavier knits generally resist holes and pilling better, but fibre and yarn quality matter as much.
- Ease of sewing. Very light jerseys can be fiddly; mid-weights are easiest on a domestic machine or overlocker.
How much fabric is in a garment
A simple T-shirt's pieces might add up to about 1.2 m², depending on size and style. On a knit with 175 cm usable width and a 10% waste allowance, the Fabric Yardage Calculator gives 0.75 m. In practice, check the layout: knit pieces must usually be cut with the greatest stretch going round the body, which limits how they can be turned.
Weight matters if you buy knits by the kilo, as many wholesalers sell them. With the dimensions tool:
- 1.5 m of 160 GSM jersey at 180 cm wide is 2.7 m², weighing 432 g (288 g per running metre);
- 1.5 m of 300 GSM fleece at the same width weighs 810 g (540 g per running metre).
At the same price per kilo, the fleece costs nearly twice as much per metre. The guide to buying fabric by the kilo explains the conversion. If a knit is sold tubular, its listed width is half the open width, so check which width the GSM and price refer to.
Knits shrink and spread
Knits, especially cotton knits, often shrink in length and spread in width in the first wash, because the loops relax from the shape they were held in during knitting and finishing. A wash test shows it clearly. Illustrative results on one sample:
- length: 50 cm before, 47 cm after: 6% shrinkage;
- width: 50 cm before, 51 cm after: the calculator reports −2%, meaning the fabric grew 2%.
Those numbers show the pattern, not a typical value. If you cannot pre-wash, cut longer by the measured length shrinkage: for a 70 cm body length at 6%, the pre-cut mode gives 74.47 cm. Better still, pre-wash knits the way the finished garment will be washed, and dry them flat or the way you will dry the garment. The guide to wash testing covers the method.
Twisting side seams
Single jersey, especially in cotton, can show spirality: after washing, the side seams of a T-shirt twist towards the front. It comes from the twist in the yarn and the way circular knitting builds the fabric, and finishing can reduce it but not always remove it. You can test for it by washing a large square sample and seeing whether it skews out of square. If it does, cut pieces strictly on the lengthwise rib line and accept a little twist, or choose a different fabric.
Fibre content
Cotton jersey is breathable and comfortable but shrinks and can lose shape. Polyester and nylon knits hold their shape, dry quickly and shrink very little, but can hold odours. Viscose and modal jerseys drape beautifully but can shrink and are weaker when wet. Elastane adds stretch and recovery; leggings and activewear typically need it. Fibre content usually changes the behaviour more than a difference of 20 GSM does.
Reading a knit listing
A useful knit listing reads something like: "95% cotton, 5% elastane single jersey, 180 GSM, 160 cm open width, 50% stretch across, pre-washed". Taking it line by line:
- Fibre content: mostly cotton, with enough elastane to recover after stretching.
- Structure: single jersey, so expect curling edges.
- Weight: 180 GSM, an everyday T-shirt weight, 5.31 oz/yd² in the converter.
- Width: open width, not tubular, so 160 cm of fabric to cut from.
- Stretch: how far the fabric extends across the width, usually as a percentage of its relaxed length. Patterns for knits state the stretch they were designed for; a fabric with less stretch than the pattern needs will make a tighter garment.
- Pre-washed: much of the relaxation shrinkage should already be out, but test anyway.
When any of these is missing, ask, or order a swatch. A swatch costs little and answers the questions no listing can, such as how the fabric feels, how opaque it is when stretched, and how it behaves in your machine.
What the tools cover
The converter gives exact GSM and ounces; the dimensions tool gives weight per running metre for kilo pricing; the yardage calculator estimates length; the shrinkage calculator turns a test into percentages and pre-cut lengths. None of them measures stretch, recovery, opacity or pilling. For those, handle a sample: stretch it, hold it to the light, and wash it.