In situ measurements of sea ice thickness (I), snow depth (S), and snow freeboard (F-sn) from drilling profile lines from 15 cruises into the Southern Ocean, Antarctica, were analyzed. I was calculated from in situ F-sn and S using an isostatic approach. I was also directly estimated from F-sn as can be obtained from laser altimetry. The root-mean-square difference (RMSD) between observed and calculated I reduces, and the correlation between F-sn and I increases substantially, when (1) using values averaged over the survey lines (approximate to 50 m) instead of single drill hole measurements (approximate to 1 m) and (2) treating positive and negative sea ice freeboard (F-i) separately. For small F-i, however, S approximates F-sn pointing toward an isostatic balance also between S and I. Our linear regression analysis between the in situ measurements suggests a direct conversion of F-sn into I using a region-specific set of equations. RMSD values are similar to those obtained employing isostatic balance models and treating positive and negative F-i separately. However, more data would have been needed to obtain significant differences between most of the various models suggested. Still our new approach gives a viable alternative for Antarctic I retrieval from altimetric measurements of F-sn alone. Correlation between in situ observations of F-sn and S is high. RMSD between observed and calculated S is small. This suggests estimation of S from altimetric F-sn measurements. Such S has an estimated precision of approximate to 5 cm, and is neither affected by snow wetness or grain size nor limited to S<50 cm.