The self inductance of a solenoid depends on its length b, area of the wire a, the area of the cross section a₁, number of turns per unit length n as

The self inductance is directly proportional to the square of the number of turns per unit length , cross section area a and length of the solenoid (b). 
$\Rightarrow \mathrm{L}={\mathrm{\mu }}_0{\mathrm{n}}^2{\mathrm{a}}_1\mathrm{b}$