This chart shows Volatility for Kellogg Company, defined to be the price range as a portion of the average price:
So, to derive the Daily Volatility on 3/2/2010 of 0.8%, the price range for the day (0.45) was divided by the average price (52.55). The Daily Volatility is obtained by dividing the daily range by the daily average. A longer Volatility period such as Weekly Volatility is obtained by dividing the weekly price range by the weekly mean price. This is a different concept from the weekly average of daily volatility.
For reference, the price is plotted in red. Volatility, as measured through various intervals, ( Daily, Weekly, Monthly and Quarterly) is plotted according to color.
Investors often make a distinction between the concept of Volatility, and the concept of Risk. Academics define them to be exactly equivalent, but as can be seen here, there is good reason to distinguish between the levels of volatility or risk experienced across different time frames. Average Daily Volatility over the history of K has been 2% in contrast to the Average Quarterly Volatility of 17%.
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