Lydersen method

${\displaystyle T_{c}={\frac {T_{b}}{0.567+\sum G_{i}-\left(\sum G_{i}\right)^{2}}}}$

Guldberg has found that a rough estimate of the normal boiling point T_b, when expressed in kelvins (i.e., as an absolute temperature), is approximately two-thirds of the critical temperature T_c. Lydersen uses this basic idea but calculates more accurate values.

${\displaystyle P_{c}={\frac {M}{\left(0.34+\sum G_{i}\right)^{2}}}}$

${\displaystyle V_{c}\,=\,40+\sum G_{i}}$

M is the molar mass and G_i are the group contributions (different for all three properties) for functional groups of a molecule.