Nick Carver Photography Blog

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What is ISO and What Does ISO Mean?

What is ISO and What Does ISO Mean?The Misconception:
What does "ISO" mean? Ask anyone seemingly "in-the-know" and they'll tell you "ISO" is an initialism for "International Standards Organization" and thus it is pronounced "eye-ess-oh." Sounds pretty convincing, but this is false.

Why This is Wrong:
There is no such thing as the "International Standards Organization." Go ahead, Google it. It doesn't exist. So then what does "ISO" stand for? Nothing. It's not an initialism or an acronym.

Allow me to explain...

Here's where the confusion comes from: although there isn't an "International Standards Organization," there is an "International Organization for Standardization." The International Organization for Standardization is a corporation based in Geneva, Switzerland that sets all sorts of international standards for manufacturing and engineering, one of which is film sensitivity in photography. Their whole deal is getting the world on the same page with standard regulations, measurements, and certifications.

Then what is "ISO?" It's this company's name, that's all. No different than "Pepsi" or "Honda." But "ISO" obviously is not an initialism or acronym because the correct acronym (in English anyway) would be IOS. So then what does ISO mean? Well, it's derived from the Greek root "isos," which means "equal" - like in "isotope" and "isosceles." And if you look at the website for the International Organization for Standardization, you'll find an explanation on why they chose this Greek root instead of an acronym to represent their company (source:

Because 'International Organization for Standardization' would have different acronyms in different languages (IOS in English, OIN in French for Organisation internationale de normalisation), our founders decided to give it the short form ISO. ISO is derived from the Greek isos, meaning equal. Whatever the country, whatever the language, the short form of our name is always ISO.

Couldn't have said it better myself.

The Truth:
So "ISO" is not an acronym. No doubt about that. It's just a company's logo written in all capital letters derived from the Greek root isos. And just like you wouldn't spell out "PEPSI" every time you ordered one, you shouldn't spell out "ISO" every time you talk about it. That's why "ISO" is correctly pronounced "EYE-so." No matter how many times you hear it pronounced "eye-ess-oh," and even though everybody and their mother says it "eye-ess-oh," it just simply isn't correct. Doesn't matter if a guy has been taking pictures for decades or working with ISO standards for 50 years, if he says it "eye-ess-oh," he's wrong.

And just for good measure, here's a video summarizing it all:

My Thoughts and Rants:
Alright, I'll be honest. For awhile I was guilty of thinking ISO stood for International Standards Organization and for years I pronounced it "eye-ess-oh." That was based partly on misinformation from an online resource (What?! You mean Yahoo Answers isn't always correct?) and mostly from my own assumptions. After all, it made perfect sense. But that's what happens when I assume. I make an ass out of u and me.

So I can't really fault people for saying it "eye-ess-oh." It's in all capital letters so it certainly looks like an acronym. And the majority of shooters say it that way even though it's incorrect. But hey, just goes to show you how quickly false information can become "fact."

My only rant on this is that a couple years back I saw on Yahoo Answers that someone posted a question asking what is ISO and what does ISO stand for. Some know-nothing do-gooder happily answered with "It stands for 'International Standards Organization.'" Seeing this error, I politely corrected the answer with the information I stated in this blog post. All was finally right in the world. But sure enough, a few days later I get a notification that someone has "improved" my answer. I go to check it out and some idiot changed it back to the wrong answer! 

Don't get your information from some dumb yahoo on Yahoo Answers. And don't let anyone try to correct you into saying it the wrong way. It's "EYE-so."

Everyone say it with me now: EYE-so!


The excellent video and audio production was done by my brother Blake Carver. Check him out at