Empirically-evaluated quantity defined by the equation $$\mathcal{T}=I{\tau }^{1/2}/(A{c}_B)=j{\tau }^{1/2}/c_{\mathrm{B}}$$ where $I$ is the electric current, $\tau$ is the transition time, $A$ is the electrode surface area, $\mathrm{B}$ is the bulk concentration of the electroactive substance $\mathrm{B}$, and $j=I/A$ is the current density.