The standard deviation is a measurement of dispersion that can be interpreted as the average deviation or spread from the mean.
It is calculated using the formula where the mean .
The Standard Deviation can be found using these steps.
You can see the formulas
if you wish.
Let's consider the name JAMES.
Letter  
J A M E S 
10 1 13 5 19 
0.400 8.600 3.400 4.600 9.400 
0.160 73.960 11.560 21.160 88.360 
Total  48  195.200 
The variation
is the result after step 4. The variation does not involve the sample
size, so we don't know if it took five numbers or fifty numbers to achieve that
variation.
Variation:
The sum of the squares of the deviations from the mean.
The variance
is what we get when we divide the variation by the degrees of freedom.
The variance doesn't have the same units as the original data, its units are
squared.
Variance:
The average squared deviation from the mean.
The standard
deviation
is found by taking the square root of the variance. This returns us
to the original units of the data and is the final measure of dispersion that
we'll use.
Standard
Deviation : The average deviation from the mean.
