  A linear relation between the hydrogen column density (N_H) and optical
extinction (A_V) in the Galaxy has long been observed. A number of studies
found differing results in the slope of this relation. Here, we utilize the
data on 22 supernova remnants that have been observed with the latest
generation X-ray observatories and for which optical extinction and/or
reddening measurements have been performed and find N_H (cm^-2) = (2.21
\pm0.09) x10^{21} A_V (mag). We compare our result with the previous studies
and assess any systematic uncertainties that may affect these results.
