An empirical design equation that relates the optimum conversions (maximum rate of reaction following the optimum temperature progression (OTP) path) to the number of continuous stirred tank reactors (CSTR) in a battery for all rates of reaction equations related exponentially to conversion (especially all simple rate equations for reversible reactions) is presented. The optimum reactor design hitherto solved through numerical iterative calculations is reduced to a highly simplified algebraic calculation. Comparative sample calculations using this new equation and the traditional matrix trial-and-error approach shows that this new method gives accurate prediction.