A new powder compaction equation which describes compaction data during the loading phase has been proposed. The equation takes the form PV=K[1-exp(-bP)]+VdP where V is the specific volume at applied pressure P, V-d is the dynamic limiting specific volume of the material, 1/b is defined as the initial yield pressure (P-0) and K is a measure of the total work of compaction. At pressures >P-d, the dynamic yield pressure of the material, a linear relation is observed between the PV and P. Pressure-volume data for high density polyethylene, polyethylene glycol 8000, starch 1500 and sodium chloride is presented to illustrate the applicability of the proposed powder compaction equation. V-d values were ca. 5% higher than values calculated from measured true densities. P-d values varied from 14.6 (polyethylene) to 93.4 (starch 1500) MPa. Starch 1500 showed the largest K value (16.3 MPa cc/g) as compared to polyethylene (7.25 MPa cc/g).