The ratio effective length of column to least radius of gyration of the column is known as slenderness ratio, and given by slenderness ratio = l/k, Where
l= effective length of the column
k= least radius of gyration of the section
The columns whose slenderness ratio is more than 80, are known as long columns and those columns whose slenderness ratio is less than 80 are known as short columns.
Euler’s formula holds good only for long columns. Euler's formula for a mild steel column is not valid if the slenderness ratio is less than 80, i.e. 60

The standard length of the shaft is
* 5 m
* 6 m
* 7 m