If there exist

${\displaystyle 10^{A}=C}$

Then

${\displaystyle \log {C}=A}$

Operation

${\displaystyle \log {ab}=\log {a}+\log {b}}$

${\displaystyle \log {\frac {a}{b}}=\log {a}-\log {b}}$

Examples

${\displaystyle \log {100}=2}$ since ${\displaystyle 10^{2}=100}$

Further reading

•  Logarithm