Sea ice salinity, density, and temperature data were used to develop new methods for determining the bulk brine volume and porosity of sea ice floes. Methods for estimating full-thickness ice sheet strength, based on large-scale field tests, are presented. The relationships among bulk sea ice properties, strain rate, and strength are illustrated. A new constitutive equation was developed for predicting the full-thickness horizontal compressive strength &sgr;c of first-year sea ice as a function of the applied strain rate and bulk porosity in the form &sgr;c=B2&egr;˙1/nϕBm where parameters B2, n, and m are about 2.7¿103, 3, and -1, respectively, and &egr;˙ and ϕB are the ice strain rate and ice floe bulk porosity of sea ice, respectively. An example of the first-year sea ice indentation force against a 90-m-wide structure is given. Estimating sea ice strength based on remote ice conductivity measurements is also discussed conceptually. ¿ 1997 American Geophysical Union