Why 120 Film Isn’t 120mm

If you’ve ever shot film (or you’re just getting started), you’ve probably noticed something odd:

We say 35mm film…
…but then we say 120 film.

Not 120mm. Just 120.

So what’s the deal?

Let's break it down. 

What does 35mm mean?

35mm film is named after its physical width.

The film strip is 35 millimeters wide, and that measurement became the name.

This comes from early motion picture film standards, where precision mattered and measurements ruled. When still photography adopted the format, the name stuck.

So when you hear 35mm film, you’re hearing a literal size.

Why isn’t 120 film called 120mm?

Because 120 isn’t a measurement.

120 film is a product name, not a size.

In the early 1900s, Kodak created standardized roll films and assigned them catalog numbers instead of dimensions. Formats like 120, 127, 620, and 220 were all part of that system.

👉 If you’re curious about the origin of those numbers, this comes directly from Kodak’s early roll film system which helped standardize photography worldwide.

Think of it like modern tech:

  • iPhone 15

  • MacBook Pro 14

These are product names, not measurements.

 

So… what size is 120 film?

Here’s where things get interesting.

  • 120 film is about 60mm wide

  • But the image size depends on the camera, not the film

That’s why 120 film is usually called medium format.

Depending on the camera, one roll of 120 film can produce different image sizes, like:

  • 6×4.5

  • 6×6

  • 6×7

  • 6×9

This flexibility is part of what makes medium format so special — and also why calling it “60mm” would’ve caused more confusion than clarity.

(If you want a deeper historical breakdown, this is commonly referred to as 120 roll film.)

What about 220 film?

220 film is the same width as 120 film.

The difference is length:

  • 220 film is roughly twice as long

  • It has no backing paper

  • It gives you about double the number of frames

Because not all cameras support it (and demand dropped over time), 220 film is mostly discontinued today but we still develop it.


The easiest way to remember film sizes

Here’s the simplest explanation we know:

35mm tells you the size.
120 tells you the format.

Or even shorter:

35mm = measurement
120 = name

Not sure what film your camera takes?
We’re always happy to help. Drop us a line.

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