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Day 10: GSM vs. OZ/LY (You're Asking for a Rug)

Welcome to Week 2, Day 10 of My Dad vs. The Algorithm.

A cartoon split-screen illustration comparing fabric weight measurements. On the left panel, titled "The Internet Spec: 400 GSM," a sweating designer wears a giant, furry, rug-like shirt with a tech pack labeled "400 GSM T-Shirt." Text reads: "Too Heavy! It's a Rug!" On the right panel, titled "The US Standard: 12 OZ/LY," Ira and Alex from Greene Textile stand in a factory holding a normal black t-shirt on a scale that reads "12.0 OZ/LY." They are smiling, and text reads: "Just Right! Streetwear Weight
Stop listening to "Internet Specs"! If you ask for a 400 GSM t-shirt, you aren't getting heavyweight apparel—you're getting a rug.

Today we are tackling the "Language Barrier" of the textile world.

I showed my dad, Ira—who has been manufacturing knit fabric in Los Angeles since 2001—a tech pack from a new brand. They wanted a "Standard Summer T-Shirt" but specified the weight as "400 GSM."

Ira’s Reaction:

"400 GSM? That’s not a t-shirt. That’s a bathroom rug. If I knit them a 400 GSM jersey, they won't be able to walk in it. It’ll weigh 2 pounds. Stop listening to TikTok experts who only talk in Grams. In Los Angeles, we speak Ounces."

Here is why mixing up these two numbers will ruin your production.

The Problem: The "Internet" uses GSM, The "US" uses OZ

If you look at specs from overseas (China, Pakistan, Portugal), they measure fabric weight in GSM (Grams per Square Meter).

But if you are producing in the USA, we measure fabric weight in OZ/LY (Ounces per Linear Yard).

They are not the same thing.

  • GSM measures a fixed square (1 meter x 1 meter).

  • OZ/LY measures the weight of a yard of fabric based on the width of the roll.

Ira’s Take:

"It’s like measuring distance in Kilometers vs. Miles. If you tell me you want '200,' but you don't tell me the unit, you're going to get something wildly different than what you expected. A 'Heavyweight' T-shirt in the US is around 12-14 oz. If you ask for 400 GSM because you think 'bigger number = better,' you are asking for something massive."

The Cheat Sheet: How to Translate

Don't guess. Use this rough translation guide to speak "American Manufacturer":

  • Lightweight Tee (Vintage feel):

    • Internet: ~135-160 GSM

    • USA (Ira): 4.5 oz – 6.0 oz/ly

  • Standard Tee (Everyday wear):

    • Internet: ~180-210 GSM

    • USA (Ira): 7.0 oz – 9.0 oz/ly

  • Heavyweight Tee (Streetwear/Boxy):

    • Internet: ~240-300 GSM

    • USA (Ira): 10.0 oz – 14.0 oz/ly

  • Heavy Fleece (Hoodies):

    • Internet: ~350-500 GSM

    • USA (Ira): 14.0 oz – 24.0 oz/ly

The Bottom Line

Don't source based on a number you saw on Instagram. Source based on Handfeel.

Ira’s Final Advice:

"Numbers on a screen can lie. A loose 10 oz feels different than a tight 10 oz. Stop trying to be a mathematician. Get a swatch, close your eyes, and touch it. If you like it, I’ll tell you what it weighs. Don't work backward from a number."

Tune in tomorrow for Day 11!

(Missed yesterday's post about the nightmare of Color Matching? Read Day 9: The "Matching Set" Headache here.)

Stop guessing the numbers. Order our Essential Swatch Kit and feel the real weight of US manufacturing.

 
 
 

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