Geotechnical Engineering

Percent Compaction Calculator

Calculate field dry density, percent compaction, density acceptance, and moisture-band status from field and Proctor test data.

Engineering schematic

Field density acceptance workflow

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

Workflow from field wet density and moisture content to field dry density, comparison with laboratory MDD, relative compaction equation, and OMC plus or minus tolerance band. — Symbols
γwet
field wet density
w
field moisture content as a decimal in the equation
γd,field
calculated field dry density
MDD, OMC
laboratory maximum dry density and optimum moisture content
RC
relative compaction

Result

Meets entered criteria: 95.5% compaction

Field dry density

112.73 pcf

Minimum required dry density

112.1 pcf

Percent compaction

95.5%

Density criterion

Pass

Moisture band

9% to 13%

Moisture criterion

Within band

Step-by-step calculation

Convert moisture content
$w=\frac{10}{100}=0.1$
Field dry density
$\gamma_{d,\mathrm{field}}=\frac{124}{1+0.1}=112.73$
Relative compaction
$RC=\frac{112.73}{118}\times100\%=95.5\%$
Minimum required dry density
$\gamma_{d,\min}=118\times0.95=112.1$
Entered moisture band
$9\%\leq w_{\mathrm{field}}=10\%\leq13\%$

What this means

The field result meets both the entered relative-compaction requirement and moisture band.

Important limitations

Acceptance must follow the project specification, test method, correction procedures, and authorized engineering judgment.

Assumptions

Field wet density and laboratory maximum dry density use the same units
The laboratory Proctor curve represents the material tested in the field
Rock corrections and project-specific acceptance rules are handled separately

Formula Used

\begin{aligned}\gamma_{d,\mathrm{field}}&=\frac{\gamma_{\mathrm{wet}}}{1+w}\\RC&=\frac{\gamma_{d,\mathrm{field}}}{\gamma_{d,\max}}\times100\%\end{aligned}

Step-by-Step Example

A field wet density of 124.0 pcf at 10.0% moisture gives 112.73 pcf dry density. Compared with a 118.0 pcf Proctor MDD, relative compaction is 95.5%.

Engineering Notes

Use the laboratory curve that represents the field material and required Standard or Modified Proctor effort.
Density and moisture may be separate acceptance criteria; a density pass does not override a moisture failure.
The calculation does not include oversize-particle corrections, test-location judgment, or method-specific bias.

FAQ

What is percent compaction?

Percent compaction, or relative compaction, is field dry density divided by the applicable laboratory maximum dry density, multiplied by 100.

Can density pass while moisture fails?

Yes. Some specifications require both a minimum relative compaction and a moisture range. The governing project requirements control acceptance.

Does the calculator apply rock correction?

No. Oversize-particle corrections and test-method limitations must be handled under the governing standard and project specification.

Related Engineering Guides

How to Calculate Percent CompactionSee the wet-to-dry density conversion and acceptance checks worked step by step.Soil Compaction TestingConnect the calculation with field methods, moisture, test locations, and corrective action.Proctor Test ExplainedUnderstand the laboratory MDD and OMC used in the comparison.