To address the sparse and inconsistent thermal expansion data previously available for almandine and spessartine garnets, this study “Revised PVT equations of state for almandine and spessartine garnets: implications for piezobarometry” establishes updated equations of state. The authors measured thermal expansion in natural garnet samples from ~90 K to ~780 K using synchrotron X-ray powder diffraction. Complementary Brillouin scattering experiments yielded adiabatic bulk moduli of 174.9 GPa for almandine and 174.0 GPa for spessartine. By combining these new measurements with literature PVT and elasticity data, the authors refined Mie–Grüneisen–Debye equations of state for both garnets. The new data demonstrate higher thermal expansion above room temperature than previously recognized, resulting in noticeably lower Debye temperatures. This revision significantly impacts host-inclusion piezobarometry, leading to lower estimated entrapment temperatures for zircon inclusions trapped in garnet. The analysis reveals no significant difference in the relative compression behavior between pure almandine and spessartine. Moreover, intermediate almandine-spessartine solid solutions display ideal mixing behavior without significant non-ideality in expansion or compression. These well-constrained models resolve long-standing uncertainties regarding garnet thermoelastic properties in metamorphic petrology. The updated parameter files are fully made available for EosFit software to support future geobarometric research.