In this review of phone cameras I came across one data point that intrigued me: They appear to write the sensor size as a fraction, in this example 1/5.8". What exactly does that mean?

My hypothesis was that it was (1/5.8)" = 0.1724" = 0.4379cm, is this correct?

And if so, why would you write it as a fraction?

  • 1
    I really do think they might mean "one five point eighth of an inch". To a non-American it is utter gobbledygook & untranslatable into 'real' numbers without your magic decoder ring, available only in US breakfast cereals ;)
    – Tetsujin
    Jan 20, 2019 at 15:40
  • It means noise at high ISO!
    – Michael C
    Jan 20, 2019 at 17:33
  • @MichaelC Show me a camera that does not take noisier images at higher ISOs:)
    – flawr
    Jan 20, 2019 at 17:40
  • @flawr OK. It means really noisy images at "high" ISOs that cameras with large sensors would consider "moderate" ISOs.
    – Michael C
    Jan 20, 2019 at 18:09

1 Answer 1


No, math is right, but not exactly correct for the sensor size. 1/5.8 inch is an obsolete method of describing the dimension of old time video tubes in early television cameras. See a Wikipedia chart of these. (it shows 1/6 inch)

That was the size of the round outer glass tube diameter then, and the contained rectangular image size was a bit smaller.

It seems like fraud to use that for digital sensor descriptions, but they do it, and 5.8 inch does sound larger. Digital video sensors have width and height dimensions in mm, like perhaps 2.4 x 1.8 mm (which sounds very small).

  • I'm no wiser. How big is 1/5.8" in real numbers?
    – Tetsujin
    Jan 20, 2019 at 15:43
  • 1
    I suspect that was part of the plan. 1/5.8" is 0.172 inch, but it is NOT the size of the current digital sensor diagonal. A very crude exaggeration at best.
    – WayneF
    Jan 20, 2019 at 15:45
  • similar to TVs being measured approximately diagonally? Oddly, even though everything else I do is metric, I still consider my big TV in the living room to be a 50", not any other 'real' set of dimensions ;)
    – Tetsujin
    Jan 20, 2019 at 15:48
  • Yes, television CRT were also measured as the outer size of their glass tube, same way, which was slightly larger than the diagonal of the picture. LCD television apparently measures the actual picture diagonal correctly. But the smallest digital sensors do not, they advertise an incorrect number. Diagonal is not fraud, if correct, it's the only way to compare size of different aspect ratios. But using a fictitious 1/5.8" number to describe a digital camcorder sensor seems very wrong.
    – WayneF
    Jan 20, 2019 at 15:56

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