What is the difference between Standard and Modified Proctor?

Standard Proctor (ASTM D698, AASHTO T 99) compacts soil in 3 layers with a 5.5 lbf (24.4 N) rammer dropped 12 in (305 mm), about 12,400 ft·lbf/ft³ (600 kN·m/m³). Modified Proctor (ASTM D1557, AASHTO T 180) uses 5 layers, a 10 lbf (44.5 N) rammer and an 18 in (457 mm) drop, about 56,000 ft·lbf/ft³ (2,700 kN·m/m³), roughly 4.5 times the energy. Modified gives a higher MDD at a lower OMC.

How do you calculate dry density from a Proctor test?

Wet density = (mass of mold + soil − mass of mold) ÷ mold volume, and dry density = wet density ÷ (1 + w). Example: 1,960 g of soil in a 944 cm³ mold is 2.076 g/cm³ wet; at 13.5% moisture the dry density is 2.076 ÷ 1.135 = 1.829 g/cm³, or 17.95 kN/m³ and 114.2 pcf.

How are OMC and MDD found?

Plot dry density against moisture content and draw a smooth curve through the points; the peak is the maximum dry density and its moisture is the optimum moisture content. This calculator fits a quadratic by least squares and takes its vertex. Use at least two points on each side of the peak.

What is the zero air voids (ZAV) curve?

It is the dry density at 100% saturation for each moisture content: γzav = Gs·γw ÷ (1 + w·Gs). No compaction point can lie above it. If one does, the specific gravity is too low or a mass, volume or moisture value is wrong. The wet side of a good compaction curve usually runs roughly parallel to the ZAV line at about 80–95% saturation.

What is relative compaction?

Relative compaction = field dry density ÷ laboratory maximum dry density × 100. Specifications often require 95% of Standard Proctor MDD (or 90–95% of Modified) within a moisture range around optimum, such as −2% to +2%.

How many data points do I need?

ASTM D698 and D1557 call for at least four points, with ideally two dry and two wet of optimum and moisture steps of about 1.5–2%. Five or six points give a better-defined peak.

What units does this calculator use?

Enter mass in grams and mold volume in cm³; moisture content in percent. Results can be shown as dry unit weight in kN/m³, dry density in Mg/m³ (g/cm³) or pounds per cubic foot. 1 Mg/m³ = 9.81 kN/m³ = 62.43 pcf.

Proctor Compaction Test Calculator

Dry density γd = γwet ÷ (1 + w). Fit a curve through 4+ points to get OMC and MDD, check every point lies left of the zero-air-voids line γzav = Gs·γw ÷ (1 + w·Gs), and relative compaction = field γd ÷ MDD × 100.

Test Configuration

Test Standard

5.5 lbf rammer, 12 in drop, 3 layers: 600 kN·m/m³

Mold Volume (cm³)

4-in mold = 944 cm³ (1/30 ft³); 6-in = 2,124 cm³

Empty Mold Mass (g)

Leave 0 if you enter soil mass only

Specific Gravity (Gs)

For ZAV and saturation (typical 2.60–2.75)

Density Unit

Curve Fit

Compaction Data Points

#	Wet Mass (g)	Moisture (%)	Dry kN/m³	Remove

Optimum Moisture Content (OMC)

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Maximum Dry Density (MDD)

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Compaction Curve

Dots = data points | Solid line = fitted curve | Dashed = Zero Air Voids (S = 100%)

Calculated Values

Point	Moisture (%)	Wet kN/m³	Dry kN/m³	Saturation (%)

Relative Compaction Check

Relative compaction = field dry density ÷ MDD × 100. Updates as you type.

Field dry density (kN/m³)

Required relative compaction (%)

Standard vs Modified Proctor

Parameter	Standard (ASTM D698 / AASHTO T 99)	Modified (ASTM D1557 / AASHTO T 180)
Rammer weight	5.5 lbf (24.4 N)	10 lbf (44.5 N)
Drop height	12 in (305 mm)	18 in (457 mm)
Layers	3	5
Blows per layer	25 (4-in mold) / 56 (6-in mold)	25 (4-in mold) / 56 (6-in mold)
Mold volume	944 cm³ (4-in) / 2,124 cm³ (6-in)	944 cm³ (4-in) / 2,124 cm³ (6-in)
Compactive effort	12,400 ft·lbf/ft³ (600 kN·m/m³)	56,000 ft·lbf/ft³ (2,700 kN·m/m³)
Methods (material passing)	A: No. 4 sieve, B: 3/8 in, C: 3/4 in (6-in mold)	A: No. 4 sieve, B: 3/8 in, C: 3/4 in (6-in mold)
Typical use	Embankments, building pads, utility backfill	Airfields, highway base and subbase, heavy loads

Energy = blows × layers × rammer weight × drop ÷ mold volume: 25 × 3 × 5.5 lbf × 1 ft ÷ (1/30 ft³) = 12,375 ft·lbf/ft³ for Standard, and 25 × 5 × 10 lbf × 1.5 ft ÷ (1/30 ft³) = 56,250 ft·lbf/ft³ for Modified. Always follow the edition of the standard named in your specification.

Summary

This Proctor Compaction Test Calculator reduces Standard (ASTM D698) or Modified (ASTM D1557) Proctor data. Enter up to ten moisture-density points and it computes wet and dry density and degree of saturation for each, fits the compaction curve, and reports the optimum moisture content (OMC) and maximum dry density (MDD) in kN/m³, Mg/m³ or pcf. A zero-air-voids line flags impossible points, and a relative-compaction check gives the field percentage and the moisture range that meets a specification.

How it works

Select Standard (ASTM D698) or Modified (ASTM D1557) and enter the mold volume (944 cm³ for the 4-in mold, 2,124 cm³ for the 6-in mold) and specific gravity Gs.
For each compaction point enter the wet mass and the oven-dry moisture content. If you weigh mold and soil together, enter the empty mold mass and it is subtracted.
Wet density = wet soil mass ÷ mold volume; dry density γd = γwet ÷ (1 + w).
A quadratic is fitted through all points, or through the peak point and its two neighbours; its vertex gives OMC and MDD.
Degree of saturation S = w·Gs ÷ e with e = Gs·γw ÷ γd − 1. Points above the zero-air-voids line (S > 100%) indicate a data or Gs error.
Enter a field dry density and the specified percentage to get relative compaction and the moisture range that meets it.

Use cases

Reducing geotechnical lab Proctor data to OMC and MDD.
Field quality control: relative compaction of embankment, subgrade and backfill from a nuclear gauge or sand-cone result.
Finding the moisture window that achieves 95% of Standard Proctor MDD.
Checking lab data against the zero-air-voids curve for the soil's specific gravity.
Comparing Standard and Modified Proctor results and units (kN/m³, Mg/m³, pcf).
Teaching and checking hand-calculated compaction curves.

Frequently Asked Questions

Last updated: 2026-10-10 · Reviewed by Nham Vu