Measurements of CO vs H₂ column densities in absorption. The green squares and blue diamonds represent the literature measurements in our Galaxy and high-z DLAs, respectively. The red pentagons and pink circles show the data obtained in this paper for LMC and SMC, respectively. The curves indicate isobaric models using the Meudon PDR code (Le Petit et al. 2006), with thermal pressures of 10⁴ (solid), 10⁵ (dashed), and 10⁶ cm⁻³ K (dotted) and metallicities of Z = 0.2 (pink), 0.5 (red), and 1 (green) relative to solar. The dashed lines indicate the standard CO/H₂ = 3.2 × 10⁻⁴ measured in the dense clouds in the MW (green) and the same value scaled to the MC average metallicity (red and purple).