Because numerous ∆G * solv (AH) models have been trained and evaluated on combinations of COSMO-RS solvation energies and experimental data, The relative centering of each distribution will change if different values are used for the solvation free energies of protons. In this work, we used the values reported in a critical evaluation by Marcus et al. , which include transfer free energies for the proton from water using the TATB assumption. We added those transfer free energies to the absolute intrinsic solvation free energy of the proton in water (-254.3 kcal mol -1 ) as also reported by Marcus. We include only solvents with "consensus" values as reported by Marcus: water, methanol, acetonitrile, dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), ethanol, For the pK a , ∆G o acid, gas (AH), and ∆G * solv (AH) values, we adopt the uncertainties from literature studies, which are described above. An unavoidable, large source of error is the proton's solvation free energy, ∆G * solv (H + ). This term anchors relative acidity scales to a single absolute energy scale, and is reliant on the choice of extrathermodynamic assumption. Uncertainties associated with this property are high, exceeding 2 kcal mol -1 in non-aqueous solvents. The uncertainty of the value in water is slightly lower, sometimes reported as under 1.5 kcal mol -1 . However, any error associated with this term manifests as a systematic offset, which can be corrected in downstream modeling applications and which usually cancels out when computing the quantities of interest in an experiment.