Geotechnical Engineering

Proctor Curve Calculator

Convert wet-density test points to dry density, plot the moisture-density relationship, and estimate optimum moisture content and maximum dry density.

Engineering schematic

Moisture–density relationship

Static symbolic figure. Enter project values in the calculator fields below.

Moisture-density chart with five representative test points bracketing a smooth peak, dry and wet sides, optimum moisture content, and maximum dry density. — Symbols
w
moisture content
γd
dry density
OMC
optimum moisture content at the bracketed peak
MDD
maximum dry density at the bracketed peak

Result

Estimated OMC 10.43%; MDD 117.16 pcf

Estimated optimum moisture

10.43%

Estimated maximum dry density

117.16 pcf

Measured maximum point

117 pcf at 10%

Points evaluated

Peak method

Three-point parabolic fit

Step-by-step calculation

Point 1 dry density
$\gamma_{d,1}=\frac{111.3}{1+0.06}=105\quad\text{at }w=6\%$
Point 2 dry density
$\gamma_{d,2}=\frac{120.96}{1+0.08}=112\quad\text{at }w=8\%$
Point 3 dry density
$\gamma_{d,3}=\frac{128.7}{1+0.1}=117\quad\text{at }w=10\%$
Point 4 dry density
$\gamma_{d,4}=\frac{128.8}{1+0.12}=115\quad\text{at }w=12\%$
Point 5 dry density
$\gamma_{d,5}=\frac{125.4}{1+0.14}=110\quad\text{at }w=14\%$

What this means

The calculated dry-density points define the entered moisture-density relationship. Confirm that the tested moisture range brackets a clear peak and review the curve shape, soil description, oversize fraction, and applicable standard before reporting OMC or MDD.

Important limitations

The fitted peak is a screening estimate. Determine reportable OMC and MDD using the governing test standard and laboratory judgment.

Assumptions

Entered densities are wet bulk densities measured for each compaction point
All points represent the same prepared soil and compactive effort
No oversize-particle correction is included

Formula Used

\gamma_d=\frac{\gamma_{\mathrm{wet}}}{1+w}\qquad \mathrm{OMC},\ \mathrm{MDD}=\operatorname*{arg\,peak}\left(\gamma_d\ \text{versus}\ w\right)

Step-by-Step Example

Five moisture-density points that bracket the peak can be converted to dry density and fitted locally to estimate the curve's OMC and MDD.

Engineering Notes

Enter wet bulk density and moisture content for each point; the calculator performs the dry-density conversion.
A reportable curve should bracket a clear peak with points on both the dry and wet sides.
The local parabolic estimate is an arithmetic check, not a substitute for the governing laboratory test procedure and curve review.

FAQ

Does the fitted peak replace the laboratory result?

No. It is a transparent screening estimate. Reportable OMC and MDD must follow the governing test standard, curve review, and laboratory procedures.

Why must the curve peak be bracketed?

If the highest dry-density point is at the end of the tested moisture range, the true optimum may lie beyond the entered points.

Should wet density or dry density be entered?

Enter wet bulk density and moisture content for each point. The calculator converts each point to dry density.

Related Engineering Guides

How to Read a Proctor CurveInterpret the dry side, wet side, curve peak, and common data problems.Proctor Test ExplainedReview test purpose, procedure, standards, and field use.Standard vs Modified ProctorCompare compactive effort and understand why the curves cannot be interchanged.