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This question already has an answer here:

I'm a big fan of point and shoot cameras, but I'm having some issues talking with friends that have DSLR. My current camera is a Sony RX-100, that's marketed as having a 1" sensor. My friend has a Canon 5D with 36x24mm sensor. Googling I found out that my camera supposedly has a 13.2x8.8mm sensor.

What's the relation between those two sensors? How is the inch value measured? (does not look to be diagonal or area or anything else my dumb mind can think of)

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marked as duplicate by mattdm, AJ Henderson, Michael Clark, John Cavan Jun 2 '13 at 23:12

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

up vote 7 down vote accepted

Your mind is working fine, it's the inch-based measurement system that's dumb.

The 36x24 mm sensor measurement is straightforward; those are the length and width of the sensor in millimeters. The 36x24 mm size happens to be the same size that the image was on 35mm film, so that size is often called "full frame".

It's the inch-based system that's confusing and unintuitive. It goes back to the time that video sensors were housed in glass tubes. The inch measurement is the diameter of the glass tube that the sensor would be housed in, if it were housed in a glass tube, which it isn't anymore.

An approximate conversion is given by Wikipedia:

Sensor formats of digital cameras are mostly expressed in the non-standardized "inch" system as approximately 1.5 times the length of the diagonal of the sensor.

Wikipedia also has a nice table of nominal sensor sizes. It says a 1" sensor is about 12.8x9.6 mm. This is reasonably close to the specification you found for your camera (it's not exactly the same, but the inch-based scheme is approximate, to sort sensors into "classes" of size, not to specify precise dimensions).

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It's also the reason why (if you're old enough to remember) your 15" LCD monitor was bigger than your 17" CRT. It's all about the tubez. – user2719 Jun 2 '13 at 15:26
At least the viewable screen size of the 15" LCD monitor was bigger than the 17" CRT. The entire 17" CRT monitor and its housing was MASSIVE compared to a 15" LCD monitor. :-) – Michael Clark Jun 2 '13 at 20:36

There really isn't a relationship between the inch designation and the actual size. Dpreview has a good explanation here:

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This is a great article. However, SE answers are designed to be self-contained, because whenever an external page gets offline, the answers renders itself content-less (and no, copying the content over is not cool as well). – igorsantos07 Jun 2 '13 at 18:50

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