**3.6. The amount of inflation**

The amount of inflation is normally specified by the logarithm of the
amount of expansion, *the number of e-foldings* *N*, given by

where the final step uses the SRA. Notice that the amount of inflation
between two scalar field values can be calculated without needing to
solve the equations of motion, and also that it is unchanged if one
multiplies *V*() by a constant.

The minimum amount of inflation required to solve the flatness and
horizon problems is about 70 *e*-foldings, i.e. an expansion by a
factor of about 10^{30}. Although this looks large, inflation is
typically so rapid that most inflation models give much more.