The Nusselt number is the ratio of convective to conductive heat transfer at the surface, so rearranging its definition gives the convective heat transfer coefficient directly.

\begin{equation}\label{eq:insulated-pipe-convection} h_{conv} = \frac{\mathrm{Nu} \cdot k_{air}}{d}\end{equation}

Symbols

\(h_{conv}\)	Convective heat transfer coefficient \([\unit{ \watt\per\meter\squared\per\kelvin}]\)
\(\mathrm{Nu}\)	Combined Nusselt number \([\unit{ \unitless}]\)
\(k_{air}\)	Thermal conductivity of air at the film temperature \([\unit{ \watt\per\meter\per\kelvin}]\)
\(d\)	Outer diameter of the surface \([\unit{ \meter}]\)