What is GSM in clothing? A fabric weight guide for blank t-shirts

Buyers ask “what GSM is this?” as if the answer settles the conversation. It does not, and it is worth knowing why before you place an order — because the same number is used to sell a promotional tee that costs $1.60 and a premium tee that costs $9, and the number alone does not tell you which one you are holding.

This guide is the working version: what GSM measures, how to convert it, what each weight band actually does on a garment, how to verify a supplier’s claim in five minutes, and where the number stops being useful.

What GSM actually measures

GSM is grams per square metre. Take one square metre of fabric and weigh it, and you have the figure. Nothing about thread count, softness, yarn quality, or where the cotton came from is included.

Two consequences follow immediately.

It measures the fabric, not the garment. A 240gsm jersey is 240 grams per square metre before it is cut. If the garment is garment-washed, it loses surface fibre and picks up shrinkage, so the finished shirt weighs slightly less than the roll it came from. A supplier who quotes 240gsm and ships a washed body at 232gsm is not necessarily lying — but “finished weight” and “greige weight” are two different promises, and only one of them is what the customer feels.

It measures quantity, not quality. 240 grams of carded cotton and 240 grams of combed long-staple cotton weigh the same. The second one is smoother, pills less, and costs more. The weight is identical; the garment is not.

How to measure GSM yourself

You do not need a lab. You need a scale that reads to 0.1 g and a ruler.

1. Cut a square from the middle of the fabric, away from seams and hems: 10 cm × 10 cm.
2. Weigh it. The result is the weight of 0.01 m².
3. Multiply by 100 to get grams per square metre.

A 10 × 10 cm square from a 180gsm jersey weighs about 1.8 g; from a 300gsm body, about 3.0 g. Kitchen scales with 0.1 g resolution are enough to tell a 180 from a 240. They are not precise enough to tell a 236 from a 240, which is why tolerances exist and why nobody should be arguing over four grams.

If you are checking a supplier’s claim, cut the square from the same place on two different pieces. Fabric weight varies slightly across a roll, and a difference between two squares from one garment is usually measurement noise rather than dishonesty.

GSM versus oz/yd²: the conversion

The United States still quotes fabric weight in ounces per square yard, and the two systems are not interchangeable by eye. The conversion factor is 33.9.

GSM	oz/yd²	Typical use
120	3.5	Promotional, event tees, very light retail
140	4.1	Light retail, summer programs
160	4.7	Standard lightweight jersey
180	5.3	Light-mid retail tee
200	5.9	Mid-weight, the safe default
220	6.5	Substantial retail tee
240	7.1	Premium basics, uniform
260	7.7	Heavy retail, boxy cuts
280	8.3	Structured streetwear
300	8.8	Heavyweight streetwear
350	10.3	Ultra-heavy, workwear-adjacent

A quick mental conversion: divide GSM by 34, or multiply ounces by 34. If a US supplier says “6.1 oz”, that is roughly 207gsm. If a Chinese supplier says 210gsm, that is roughly 6.2 oz. Treat anything within about 5% as the same weight, because both numbers are rounded.

The weight bands, and what each one does

120–160gsm: promotional

Light, cheap to produce, and usually the right choice for an event where the shirt will be worn once and then become a cleaning rag. Print quality is acceptable for one colour; a full-front photographic print on 140gsm looks cheap because the fabric shows through the ink.

At this weight, opacity becomes a real constraint. A dark print on a white 140gsm tee is fine. A white print on a dark 140gsm tee needs a heavy underbase that stiffens the whole front panel, and the shirt starts to feel like a printed panel rather than a garment.

180–220gsm: retail

The band where most brands live, and for good reason. At 200gsm the fabric is opaque enough for a dark print, light enough to wear in summer, stable enough to hold a screen-print edge, and priced so the retail math works.

This is also the band where yarn quality shows most clearly. A 200gsm combed jersey and a 200gsm carded jersey feel like different products in the hand and wash differently: the carded one develops a fuzzy surface within five washes, the combed one does not.

230–260gsm: premium basics

The weight that reads as “substantial” without announcing itself. A 240gsm tee holds a straight side seam, keeps its shape through a season, and takes a heavier ink deposit than 200gsm without going stiff.

This is the natural home for a brand selling at $35–$60 retail, because the customer can feel the difference on the hanger and it survives more washes. It is also where the fit decision starts to matter more than the weight: at 240gsm a relaxed body drapes, and the same relaxed body at 300gsm stands away.

280–350gsm: structured streetwear

Heavy single jersey at this weight behaves as a structure rather than a drape. The body holds a wide shape without sagging, a dropped shoulder looks deliberate rather than sloppy, and a thick ink deposit cures without the edges cracking.

The cost is a firm hand out of the bag. A 350gsm body that has not been garment-washed feels stiff for the first few wears; washing softens it by roughly one weight step. That is why heavy blanks are so often sold washed — the softened version is what most streetwear brands actually approve.

What weight changes, in practice

Drape and silhouette

Weight sets how the garment falls. Light jersey follows the body and shows the shape underneath; heavy jersey holds a line and hides it. If your fit is boxy, heavier fabric holds the box; if your fit is classic, a heavy body reads as oversized even when the pattern is not.

Opacity

Below about 170gsm, a white shirt against a dark background shows the print and sometimes the body. Above 200gsm, white-on-white layering stops being a problem. If your product is a white tee with a large dark print, the print will show through the back at 140gsm and will not at 220gsm.

Print behaviour

A stable, heavier surface lets the printer lay a thicker film without the fabric deforming under the screen. On a 160gsm jersey, the knit stretches as the squeegee passes and the print cracks at the edge after a few washes — not because the print is wrong, because the base moved.

Shrinkage

Weight and shrinkage are independent, but they get confused constantly. A 300gsm body that was never pre-shrunk can move 5% on the first wash; a 180gsm body that was pre-shrunk moves 1–2%. If you are comparing two suppliers, ask both for the shrinkage figure, not the weight.

Cost

More cotton per square metre costs more, and heavier fabric also takes longer to knit and to dry after washing. Between 180gsm and 300gsm, expect the fabric cost per garment to roughly double. That is the single largest line in the price of a blank — larger than the decoration on a simple one-colour print.

How to choose a weight, by use case

Product	Weight	Why
Event or promotional tee	140–160gsm	Cost per unit dominates; print is one colour
Retail tee, first SKU	200gsm	Opaque enough, light enough, priced to sell
Premium basics	240–260gsm	Reads substantial, holds shape, survives a season
Streetwear, boxy fit	280–340gsm	Holds the silhouette, takes a heavy print
Uniform and workwear	220–260gsm	Balances durability with wearability in heat
Hoodie / crewneck	300–400gsm fleece	See the hoodie guide: fleece weights work differently

The GSM traps worth knowing

The label weight is not the fabric weight. A tag says “6.0 oz” because it is marketing copy, not a measurement. Ask for the specification sheet.

Washed garments lose a few grams. Garment washing removes surface fibre. A 260gsm washed tee might spec at 250gsm finished. That is normal; what is not normal is a 15% drop.

Fleece GSM and jersey GSM are not comparable. 350gsm fleece feels thinner in the hand than 300gsm jersey, because fleece is a brushed knit with air in it. Comparing across fabric families with the same number is a common purchasing mistake.

A heavier shirt is not always a warmer shirt. Warmth depends on the fibre and the trapped air, not just the mass. A 260gsm cotton tee is cooler than a 240gsm cotton-poly blend in humid weather.

“Double yarn” is not a weight. It is a construction that raises density at the same nominal weight. A 240gsm double-yarn jersey feels denser and more opaque than a 240gsm single-yarn jersey, and the numbers will not tell you that.

The four variables that move hand feel more than 20gsm

If you line up four 200gsm jerseys and hand them to a buyer, they will rank them by feel and get it wrong about what they are ranking. Weight is held constant, so what is left is yarn, gauge, stitch and finish.

Yarn count and type. A finer, combed yarn at 200gsm knits into a smoother, denser surface than a coarser carded yarn at the same weight. The carded version has more short fibres sticking out of the surface, which is why it feels fuzzier in the hand and looks older sooner.

Knit gauge. Gauge is needle density on the machine. A finer gauge produces a tighter loop and a smoother face; a coarser gauge produces a more open, slightly textured face. Two 260gsm fabrics at different gauges read as two different products — one as a premium basic, one as a workwear body.

Stitch length. Loops per centimetre, essentially. A tighter stitch makes a denser fabric with less stretch; a looser stitch feels softer and drapes more but loses shape faster at the neckline and hem.

Finishing. Garment washing, enzyme treatment and silicone wash all change the surface without changing the weight much. A washed 240gsm and an unwashed 240gsm differ more in the hand than a washed 240gsm and an unwashed 260gsm.

This is the practical reason a supplier who answers only “240gsm” has answered about a quarter of the question. Ask for the yarn and the finish in the same breath.

A worked comparison: the same design at three weights

Take one product — a boxy tee, two-colour front print, sold at $45 retail — and specify it three ways.

At 200gsm. The garment drapes, the print sits on a stable enough surface to cure cleanly, and the cost per unit leaves room for margin. The risk is that at 200gsm a boxy body reads as a slightly wide regular tee rather than a deliberate oversized cut, because the fabric follows the body instead of holding away from it.

At 240gsm. The boxy shape starts to read as intended. The print is unchanged technically, but it looks denser because the surface under it is more opaque. Cost rises by roughly 20–25% on the fabric line, and the retail price usually supports it.

At 300gsm. The shape is unmistakably oversized, the print looks thick because the garment is thick, and the hand is firm until the first wash. Cost rises again. At this point the constraint is not the fabric but the customer: a 300gsm tee is a different product proposition from a 200gsm one, and the marketing has to carry that.

The lesson is not that heavier is better. It is that weight is part of the design brief, and choosing it late — after the print is approved, or after the price is set — is how a program ends up with a garment that photographs well and sells badly.

How washing changes the numbers

A finished garment weighs less than the fabric it was cut from, and the gap is bigger than most buyers expect.

Garment washing removes surface fibre, relaxes the knit and shrinks the garment. On a 260gsm body, a wash program can take off 2–4% of the fabric weight before the garment is even packed. That is why a specification sheet that says “260gsm” and a finished shirt that measures 252gsm are not in conflict: one is the roll, the other is the shirt.

Two practical consequences follow.

First, ask what the quoted figure refers to. “Finished weight” and “greige weight” differ by a few percent, and a supplier quoting greige while a competitor quotes finished looks heavier without being better.

Second, do not re-weigh after ten home washes and call it a discrepancy. Cotton continues to lose surface fibre and to shrink through the first several washes. A measurement taken after five washes is not a check on the supplier; it is a check on how the garment ages, which is a different and more useful question.

Fleece, interlock and the weight numbers that do not compare

Weight figures are only comparable inside the same fabric family. A 350gsm fleece and a 350gsm single jersey are not the same product in the hand, and comparing them numerically is misleading.

Fleece is a knitted base with a brushed inside; the brush raises fibre and traps air, so 350gsm fleece feels softer and lighter in the hand than 350gsm jersey. That is why hoodie specifications are usually given as two numbers — the face weight and the total — or quoted in ounces with the brushing implied.

Interlock is a double knit: two sets of loops, one on each face. At the same gsm it is denser, smoother and less stretchy than single jersey. A 200gsm interlock reads as a more expensive fabric than a 200gsm jersey, and it is, because twice as many loops are knitted per square metre.

If you are comparing quotes across fabric families, compare the finished garment and the sample, not the number.

Weight and price: where the money actually goes

Fabric is the largest cost line in a blank t-shirt, and weight is the largest driver of fabric cost. Between 180gsm and 300gsm the fabric cost per garment roughly doubles; between 180gsm and 240gsm it rises by roughly a third.

Two things sit on top of that.

Knitting and drying time. Heavier fabric runs slower through the knitting machine and takes longer to dry after dyeing or washing. That is a real cost, and it does not show up in the gsm figure.

Yield loss. Heavy fabric is stiffer on the cutting table, which usually means slightly more waste per garment than a light jersey. On a large program, one percent of waste is worth arguing about.

What does not change much with weight is decoration cost. A screen print costs the same whether the body is 180gsm or 300gsm, unless the lighter body forces a different mesh or a heavier deposit to look solid. That asymmetry — fabric scales with weight, decoration does not — is why a heavy blank changes the price of a plain tee far more than the price of a three-colour printed one.

What to ask a supplier, in order

1. What is the fabric weight, finished, in gsm?
2. What is the yarn — combed, carded, long-staple?
3. What is the shrinkage on the first wash, and was it pre-shrunk or garment washed?
4. What knit is it — single jersey, interlock, fleece? At what gauge?
5. Can you send a sample so I can cut a 10 cm square and weigh it?

Those five questions separate a supplier with a specification sheet from one with a price list. The weight is the first question, not the only one.

Where weight stops mattering

At some point the buyer stops being able to tell. Most people cannot distinguish 220gsm from 240gsm in the hand without a scale, and almost nobody can tell 300 from 320. What they can tell is whether the collar collapsed, whether the shirt shrank, and whether the print cracked.

That is the practical lesson: spend your attention on the four things a customer will notice — collar construction, pre-shrinking, print adhesion, and dye consistency — and treat GSM as the entry ticket to the conversation rather than the answer to it.

If you are specifying a program now, the fabric page lists the eight fabrics we knit with their weights, hand feel, printing notes and shrinkage, and the t-shirt buying guide walks through the rest of the specification.