Wool Super Numbers: What 100s, 120s and 150s Actually Measure
A super number measures fiber fineness, nothing else. It counts how many 560-yard hanks of yarn can be spun from one pound of combed wool, and it maps to a maximum fiber diameter: Super 100s is 18.75 microns, 120s is 17.75, 150s is 16.25. Finer means softer and more lustrous, and also more delicate, so the everyday sweet spot is Super 110s to 130s.
The super number is the most misread label in tailoring, because it looks like a quality rank and behaves like one in the shop. A Super 150s suit costs more than a Super 100s suit, feels softer in the hand, and drapes more fluidly. The shop assistant will tell you it is better. It is better at exactly one thing, and worse at the thing that decides whether the suit survives two years of weekly wear.
The number measures fiber fineness, and only fiber fineness. It counts how many 560-yard hanks of yarn can be spun from one pound of combed wool, and more hanks means finer yarn, which maps to a thinner fiber diameter in microns. The scale is overseen by the International Wool Textile Organization, and the numbers are maximum diameters, not averages: Super 100s is 18.75 microns, 110s is 18.25, 120s is 17.75, 130s is 17.25, and 150s is 16.25.
Finer is softer, and more fragile
A finer fiber is, by definition, a thinner and more fragile one. The cloth it makes is softer, smoother, and more lustrous, with a fluid drape that a coarser cloth cannot match. That is a real upside, not marketing. The catch comes at the top end: once you go much beyond Super 130s, the cloth turns delicate, creases more easily, shines at the stress points sooner, and wears out faster.
The trade-off is mechanical. Dropping fiber thickness below 17.5 microns, the boundary between Super 120s and the ultra-fine tiers, sacrifices the cortical mass that resists daily abrasion. Fabrics meant for daily wear need to survive 20,000 to 30,000 rubs on the Martindale test, a threshold delicate ultra-fine wools struggle to meet. A Super 150s suit feels gorgeous in hand and rewards gentle wear and occasional outings. A Super 120s twill in regular rotation will outlast it by years.
The number is not the weight, or the quality
The single most common confusion is mistaking the super number for fabric weight. It is not. A Super 150s cloth can be woven heavy or light, and a high super number does not mean a cooler fabric, even though finer fibers feel lighter in the hand. Weight is measured separately, in grams per square meter, and it is the number that decides whether a suit works in July or January.
Nor is the number a quality rank. A tightly woven Super 120s twill is more resilient and wrinkle-resistant than a loosely woven Super 180s plain weave, because its thicker yarns have better shape retention. The weave, the finishing, and the mill matter as much as the fiber. And the word Super itself is regulated: under international convention it can only be applied to fabrics made of new, pure wool, while blends with cashmere or silk use the S designation instead.
What to buy for which suit
For a suit you will wear once or twice a week, buy Super 110s to 130s. It is fine enough to look and feel excellent, robust enough to last years, and the range tailors consistently recommend for regular rotation. Super 100s is the workhorse below that: sturdier, more matte, honest, and the right pick for a suit that will be dry-cleaned often and worn hard.
Save 150s and above for occasion suits, weddings, and special events, where the suit is worn a few times a year and the drape matters more than the durability. And remember the real multiplier: fit. A cut-to-you Super 120s beats an off-the-rack Super 150s every time, because the number on the label never fixed a bad shoulder.
Related reading
Two earlier posts on this site cover ground “Wool Super Numbers: What 100s, 120s and 150s Actually Measure” builds on: Super 120s vs Super 150s: The Fineness Trade Nobody Tells You About, Real Silk vs Polyester Satin: The Burn Test Settles It in Ten Seconds, and Real Linen vs a Blend: The Tests That Tell Them Apart in the Store.
Frequently asked questions
What does Super 120s mean in a suit?
It means the wool fibers are at most 17.75 microns in diameter, spun fine enough that 120 hanks of 560 yards each can be spun from one pound of combed wool. The number measures fiber fineness only, not fabric weight or overall quality.
Is a higher super number better?
It is softer and more lustrous, but less durable. Past Super 130s, the cloth creases more, shines at stress points sooner, and wears out faster. For a suit in regular rotation, Super 110s to 130s is the sweet spot, and 150s and above belong on occasion suits.
What is the difference between Super 100s and Super 150s?
About 2.5 microns of fiber diameter: 100s is 18.75 microns, 150s is 16.25. That small difference changes how the cloth behaves: the 150s drapes more fluidly and feels softer, while the 100s is sturdier, more matte, and far more durable for weekly wear.
Does super number tell you how heavy a suit fabric is?
No. Weight is measured separately in grams per square meter, and a high super number does not mean a cooler or lighter fabric. The super number measures fiber diameter only, so check the weight separately when choosing a suit for summer or winter.