Reply to comment on ‘electric polarizabilities of CH ₄ , CO, and O ₂ determined by an optical refractometer’

Abstract We respond to the comment by Egan on our paper (2026 Metrologia 63 025007). We acknowledge that, due to the inadvertent use of molecular magnetic susceptibility data from the literature expressed in cgs units without conversion to SI units, the results for the electric polarizability in the original paper require correction. As the magnetic susceptibility of O 2 is large, its correction is about 0.275%, leading to a revised value of 3.947 33(19) cm 3  mol − 1 . For CH 4 and CO, whose magnetic susceptibilities are much smaller, the corrections are below 1 × 10 − 5 , resulting in revised values of 6.440 39(30) cm 3  mol − 1 and 4.881 51(24) cm 3  mol − 1 , respectively. We also provide clarification on each of the four points raised in the comment, including the relevance of microwave absorption, the two-color measurement comparison, and the long-term stability of the Fabry–Pérot cavity deformation coefficients. All other conclusions of the original paper remain unchanged.