Entropy of a discrete random variable with possible values {x1 x2, ..., xn} and probability density function P(X) is:
\(H\left( X \right) = - \mathop \sum \limits_{i = 1}^n P\left( {{x_i}} \right){\log _{\rm{b}}}P\left( {{x_i}} \right)\)
The value of b gives the units of entropy. The unit for b = 10 is:
1
bits
2
bann
3
nats
4
deca