What is the difference between Standard and Modified Proctor?

Standard Proctor (ASTM D698) uses 12,400 ft-lb/ft³ of compaction energy with a 5.5 lb hammer dropped 12 inches, while Modified Proctor (ASTM D1557) uses 56,000 ft-lb/ft³ with a 10 lb hammer dropped 18 inches. Modified Proctor yields higher MDD and lower OMC.

What is dry unit weight?

Dry unit weight (γd) is the weight of dry soil solids per unit volume of the total soil mass. It is calculated as γd = γwet / (1 + w), where γwet is the bulk unit weight and w is moisture content as a decimal.

What is the Zero Air Voids (ZAV) curve?

The ZAV curve represents the theoretical maximum dry density at each moisture content assuming no air voids (100% saturation). Actual compaction curves always lie to the left of and below the ZAV curve. It is computed as γd_zav = Gs × γw / (1 + Gs × w).

How many data points do I need?

A minimum of 4 points is required to define a reliable compaction curve. Five or six points spanning both wet and dry of optimum give a better peak definition. ASTM D698/D1557 require at least 4 compaction points.

What units does this calculator use?

The calculator works in kN/m³ for unit weight. You input mass in grams and mold volume in cm³; the tool converts internally. Moisture content is entered as a percentage (e.g., 12 for 12%).

Proctor Compaction Test Calculator

Enter mold measurements and wet soil weights for each compaction point to get dry unit weight, plot the curve, and find OMC and MDD.

Test Configuration

Test Standard

Mold Volume (cm³)

4-inch mold ≈ 944 cm³

Specific Gravity (Gs)

For ZAV curve (typical 2.60–2.75)

Compaction Data Points

#	Wet Soil Mass (g)	Moisture Content (%)	Dry Unit Weight (kN/m³)

Optimum Moisture Content (OMC)

—

Maximum Dry Density (MDD)

—

kN/m³

Compaction Curve

Blue dots = data points | Blue line = fitted curve | Dashed = Zero Air Voids (ZAV)

Calculated Values

Point	Moisture Content (%)	Wet Unit Weight (kN/m³)	Dry Unit Weight (kN/m³)

Summary

Enter mold measurements and wet soil weights for each compaction point to get dry unit weight, plot the curve, and find OMC and MDD.

How it works

Select Standard or Modified Proctor test type.
Enter the mold volume and the number of data points (typically 4–6).
For each point, enter the wet soil mass and moisture content percentage.
The calculator converts wet density to dry unit weight using the formula: γd = γwet / (1 + w).
The compaction curve is plotted and the peak is identified as the optimum moisture content (OMC) and maximum dry density (MDD).
Zero-air-voids (ZAV) curve is overlaid using specific gravity for reference.

Use cases

Geotechnical lab analysis of soil compaction characteristics.
Field quality control for earthwork, embankments, and road subgrade.
Determining compaction specifications for construction projects.
Academic study and verification of Proctor test calculations.
Comparing Standard vs Modified Proctor compaction results.
Cross-checking hand-calculated lab data against plotted curves.

Frequently Asked Questions

Last updated: 2026-09-20 · Reviewed by Nham Vu