# neper (Np)

The neper (Np), named for the mathematician James Napier,
is a unit used to express the ratio of quantities such as current or voltage. Thus the ratio *N*, in
nepers, of current *I*_{1} and *I*_{2} is *N* = ln(I_{2}/I_{1}). The neper is thus
the natural logarithmic equivalent (see logarithm)
of the decibel. Power ratios, say of powers *P*_{1} and *P*_{2}, can also be expressed
in nepers; here *N* = ½ ln (*P*_{2}/*P*_{1}),
and 1 neper = 8.686 dB.