This paper presents new calibrations of stellar parameters for O stars at solar metallicity, accounting for non-LTE effects, stellar winds, and line-blanketing. The calibrations are derived using two methods: an observational scale based on spectroscopic analyses of a sample of massive stars, and a theoretical scale derived from non-LTE spherically extended models computed with the CMFGEN code. The main findings include: 1. **Effective Temperature Scales**: The effective temperature scales for dwarfs, giants, and supergiants are cooler by 2000 to 8000 K compared to previous calibrations, with the theoretical scale being slightly cooler than the observational one. The reduction is most significant for early spectral types and supergiants. 2. **Bolometric Corrections**: Bolometric corrections are reduced by 0.1 mag due to line blanketing, which redistributes UV flux to the optical range. For a given spectral type, the reduction is larger for early types and supergiants. 3. **Luminosities**: Luminosities are reduced by 0.20 to 0.35 dex for dwarfs, by approximately 0.25 for giants, and by 0.25 to 0.35 dex for supergiants. The reduction is consistent for both temperature scales and is independent of spectral type for giants and supergiants, slightly larger for late-type dwarfs. 4. **Lyman Continuum Fluxes**: Lyman continuum fluxes are also reduced. The theoretical values for hydrogen ionizing photon fluxes for dwarfs are 0.20 to 0.80 dex lower than those of Vacca et al. (1996), with larger reductions at late spectral types. For giants, the reduction is 0.25 to 0.55 dex, while for supergiants, it is 0.30 to 0.55 dex. The new calibrations represent a significant improvement over previous ones, particularly in the treatment of non-LTE line-blanketing in the expanding atmospheres of massive stars. The results are crucial for understanding the properties of massive stars, including their role in enriching the interstellar medium, creating H ii regions, and influencing star formation and supernova explosions.This paper presents new calibrations of stellar parameters for O stars at solar metallicity, accounting for non-LTE effects, stellar winds, and line-blanketing. The calibrations are derived using two methods: an observational scale based on spectroscopic analyses of a sample of massive stars, and a theoretical scale derived from non-LTE spherically extended models computed with the CMFGEN code. The main findings include: 1. **Effective Temperature Scales**: The effective temperature scales for dwarfs, giants, and supergiants are cooler by 2000 to 8000 K compared to previous calibrations, with the theoretical scale being slightly cooler than the observational one. The reduction is most significant for early spectral types and supergiants. 2. **Bolometric Corrections**: Bolometric corrections are reduced by 0.1 mag due to line blanketing, which redistributes UV flux to the optical range. For a given spectral type, the reduction is larger for early types and supergiants. 3. **Luminosities**: Luminosities are reduced by 0.20 to 0.35 dex for dwarfs, by approximately 0.25 for giants, and by 0.25 to 0.35 dex for supergiants. The reduction is consistent for both temperature scales and is independent of spectral type for giants and supergiants, slightly larger for late-type dwarfs. 4. **Lyman Continuum Fluxes**: Lyman continuum fluxes are also reduced. The theoretical values for hydrogen ionizing photon fluxes for dwarfs are 0.20 to 0.80 dex lower than those of Vacca et al. (1996), with larger reductions at late spectral types. For giants, the reduction is 0.25 to 0.55 dex, while for supergiants, it is 0.30 to 0.55 dex. The new calibrations represent a significant improvement over previous ones, particularly in the treatment of non-LTE line-blanketing in the expanding atmospheres of massive stars. The results are crucial for understanding the properties of massive stars, including their role in enriching the interstellar medium, creating H ii regions, and influencing star formation and supernova explosions.