The degree of compression sustained by the solar wind field as it convects to the magnetopause has been determined empirically with magnetometer data from ISEE 3 in the solar wind and ISEE 1 in the magnetosheath. At the stagnation point, the strength BSH of the magnetosheath field may be expressed as BSH=(4 BSWBST)1/2, which implies that BSH is equal to the geometric mean of the stagnation field strength BST and the shocked solar wind field, approximated by 4 BSW'. For the usual spiral pattern of the solar wind field, BSH on the duskside of the magnetopause is about 20% stronger than it is on the dawnside. No dependence of BSH on the sign of the north-south component of the solar wind field is apparent.