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How we measure cloud amounts

In meteorology, cloud cover is measured in oktas, or eighths of the sky.

If you look up at the sky, and mentally divide it into eight boxes, then imagine all the cloud you can see squashed into these boxes. How many boxes does the cloud fill? This is how many oktas of cloud there are.

  • 0 oktas represents the complete absence of cloud

Photograph of a cloudless blue sky

  • 1 okta represents a cloud amount of 1 eighth or less, but not zero

Photograph of rolling hills and blue sky with a small amount of cumulus clouds

  • 7 oktas represents a cloud amount of 7 eighths or more, but not full cloud cover

Photograph of a cloudy sky with just a few glimpses of blue visible in the cloud breaks

  • 8 oktas represents full cloud cover with no breaks

Photograph of the sea with a completely cloudy, grey sky

We also use terminology to convey generally how cloudy it is, for example scattered cloud refers to 3 to 4 oktas where about half the sky is covered, broken cloud is 5 to 7 oktas where much of the sky is covered and overcast is 8 oktas of cloud with no breaks in the cloud at all.

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This article is from the free online course:

Learn About Weather

University of Exeter

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