The $f_{\mathrm{T}}$ of a $\text{BJT}$ is related to its $g m, \mathrm{C}_\pi$ and $\mathrm{C}_\mu$ as follows
- $f_{\mathrm{T}}=\frac{\mathrm{C}_\pi+\mathrm{C}_{\mu}}{g_\text{m}}$
- $f_{\mathrm{T}}=\frac{e \pi\left(\mathrm{C}_\pi+\mathrm{C}_\mu\right)}{g_m}$
- $f_{\mathrm{T}}=\frac{g_\text{m}}{C_\pi+\text{C}_\mu}$
- $f_{\mathrm{T}}=\frac{g_\text{m}}{2 \pi\left(\mathrm{C}_\pi+\mathrm{C}_{\mu}\right)}$