'Quarter-range' rule of thumb

The complexity of the standard deviation's formula makes its value difficult to interpret. A simple rule-of-thumb is that, for many data sets, the standard deviation is just under a quarter of the range.

The 70-95-100 rule of thumb

A more accurate rule-of-thumb is called the 70-95-100 rule. In many distributions,

For skew data, or data sets with long tails, outliers or clusters the 70-95-100 rule is often less accurate.

Examples

Hours of sunshine in Gaborone

The mean and standard deviation are only reasonably 'complete' summaries of the shape of a distribution when it is fairly symmetric.