Compaction Quick-Check Calculator

Checks a density gauge reading against the Proctor: dry density, percent compaction, moisture deviation from optimum, and the wet density the operator needs to hit. Runs entirely offline; inputs persist in this browser via localStorage.

Use limits: This checks arithmetic, not soil. The correct Proctor curve for the material actually in the trench, oversize (rock) correction, gauge calibration, and probe depth are all upstream of this math — and the testing agency's report is the document of record. This tool is for arguing productively at the trench, not for acceptance.

Gauge Reading

Gauge output

Most gauges display both — enter whichever pair you trust.

Wet density (pcf)

Moisture content (%)

Proctor & Spec

Max dry density (pcf)

From the lab Proctor for this material — confirm the curve number matches the soil in the hole.

Optimum moisture (%)

Required compaction (%)

Moisture tolerance (± % of optimum) — optional

Enter if the spec has a moisture window (e.g. optimum ±2%). Leave blank if it only specs density.

—

Dry density	—
Percent compaction	—
Margin vs. required	—
Moisture vs. optimum	—
Wet density needed at this moisture	—

How the Numbers Are Derived

The math

Dry density from a wet reading:

γ_dry = γ_wet / (1 + w/100)

Percent compaction:

RC = γ_dry / γ_dry,max × 100

Wet density required to pass at the current moisture (the number to give the roller operator):

γ_wet,req = (RC_req/100) × γ_dry,max × (1 + w/100)

Why moisture matters even when the density passes

Wet of optimum in clays: the lift may pass density today and pump under the next lift or the pipe zone tomorrow. Most specs with a moisture window exist for this reason.
Dry of optimum: some soils (especially clays) hit density dry but stay in a brittle, high-suction state that collapses on wetting — a real problem under slabs and structures.
If the reading is far from optimum, the honest question is whether the material can even reach the required density at that moisture — check where the gauge moisture sits on the Proctor curve.

When percent compaction comes back over 100%

Not physically impossible (field compaction energy can exceed the standard Proctor), but over ~102–103% deserves suspicion before celebration:

Wrong Proctor curve for the material actually in the hole — the most common cause.
Oversize particles: gravel and cobbles read dense. If more than ~5% of the material is retained on the ¾-in. sieve, an oversize correction (ASTM D4718) applies and the raw comparison is invalid.
Standard (D698) vs. modified (D1557) Proctor mix-up — modified max densities run several pcf higher.

References

ASTM D698 / D1557 — Standard and Modified Proctor laboratory compaction. https://www.astm.org/

ASTM D6938 — In-place density and water content by nuclear methods.

ASTM D4718 — Correction of unit weight and water content for soils containing oversize particles.