The size listed on the original tag may not be an accurate indication of the fit. "Fits like Men's" and "Fits like Women's" are estimates of modern sizes based on the measurements of the sweater.
The chest/bust size and length measurements are the only 100% accurate way to estimate the fit.
Chest/bust size is equal to the width of the sweater multiplied by two. For example, the sweater shown here has a chest width of 19", which would give it a chest/bust size of 38".
The length measurement is taken from the top of the sweater to the bottom hem.