We provide the conversion parameters to allow a 3He melting curve thermometer to be used to calibrate secondary thermometers to the PLTS2000 temperature scale (Rusby et al. in J Low Temp Phys 149(3):156, 2007). Additional fits to the phase diagram of superfluid 3He are also provided using the melting curve P, T measurements and of the phase diagram of superfluid 3He (Greywall in Phys Rev B 33(11):7520, https://doi.org/10.1103/PhysRevB.33.7520, 1986) as a bridge. Further, the melting curve measurements of Osheroff and Yu (Phys Lett A 77(6):458, https://doi.org/10.1016/0375-9601(80)90539-3, 1980) are also used to extend the scale below 0.9 mK. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.