The elevation in its boiling point is directly proportional to the molality of the solution When a non-volatile solute is added to a volatile solvent. 

$∆{\mathrm{T}}_{\mathrm{b}}=\left({\mathrm{T}}_{\mathrm{b} }^{\text{'}}-{\mathrm{T}}_{\mathrm{b}}\right)$

$∆{\mathrm{T}}_{\mathrm{b}} \mathrm{\alpha } \mathrm{molality}$

$∆{\mathrm{T}}_{\mathrm{b}} =\mathrm{i}\times {\mathrm{K}}_{\mathrm{b}}\times \mathrm{molality}$

${\mathrm{K}}_{\mathrm{b}}=$Molal elevation constant

So, $\mathrm{molality}=\frac{∆{\mathrm{T}}_{\mathrm{b}}}{{\mathrm{K}}_{\mathrm{b}}}$

Hence, the molal elevation constant is the ratio of Elevation in boiling point to molality.