Compaction Test Calculator

This calculator reduces raw Proctor compaction test measurements — the wet weight of soil packed into a standard mold, at a known moisture content per ASTM D698 (Standard Proctor) or ASTM D1557 (Modified Proctor), with moisture content itself measured per ASTM D2216 — into the density and void metrics geotechnical engineers use to judge compaction quality. Wet density is simply the specimen's weight divided by the mold volume (the standard Proctor mold is 1/30 ft³); dividing that by (1 + w), where w is moisture content as a decimal, strips out the water's weight to get dry density, γd = γwet/(1+w) — the number actually compared against a project's maximum dry density specification (commonly 95% of Proctor maximum in the field). From dry density and the soil's specific gravity Gs, the calculator backs out the void ratio, e = (Gs·γw/γd) − 1, where γw is water's unit weight (62.4 pcf) — a lower void ratio means the soil grains are packed more tightly with less air/water space between them.

Degree of saturation, S = (w·Gs)/e × 100, then expresses what fraction of those voids are actually filled with water rather than air, capped at 100%. The zero-air-void density is a theoretical ceiling: the maximum dry density physically possible at that moisture content if every void were saturated, useful as a reference curve alongside your compaction curve to flag results that would imply an impossible (negative-air-void) condition. This tool only computes point values from one test — it doesn't determine the true Proctor maximum dry density or optimum moisture content, which require running the full multi-point compaction curve.