In geography, an okta is a unit of measurement used to describe the amount of cloud cover at any given location such as a weather station. The unit of cloud amount – okta – is an eighth of the sky dome covered by cloud. Sky needs to be mentally divided into eight boxes, then all the visible clouds are squashed into these boxes. The number of filled boxes is how many oktas of cloud there are. Cloud amounts are generally rounded up to the next okta. For example, ‘2 and a bit’ oktas is rounded to 3 oktas. The exception is when more than 7 but less than 8 oktas is observed – in this instance, cloud amount is rounded down to 7 oktas. Oktas are often referenced in aviation weather forecasts and low-level forecasts. The following is the okta scale:

• 0 oktas represents the complete absence of cloud.
• 1 okta represents a cloud amount of 1 eighth or less, but not zero.
• 2 oktas represent a cloud amount of 2 eighths.
• 3 oktas represent a cloud amount of 3 eighths.
• 4 oktas represent a cloud amount of 4 eighths.
• 5 oktas represent a cloud amount of 5 eighths.
• 6 oktas represent a cloud amount of 6 eighths.
• 7 oktas represent a cloud amount of 7 eighths or more, but not full cloud cover.
• 8 oktas represent full cloud cover with no breaks.
• 9 oktas represent sky obscured by fog or other meteorological phenomena.