Some specifications ask for compacted fill at a percentage of a laboratory test result, not at a fixed density. Ohio’s highway agency uses 95 percent for one part of its work. Here is what that number measures.
A Proctor test is a laboratory method that finds a soil’s maximum dry density and optimum moisture content. A 95 percent Proctor specification sets the field target at 95 percent of that lab maximum. Ohio’s highway agency (ODOT) uses 95 percent for the top 8 inches of foundation. That figure comes from one state specification, not a universal rule.
What a Proctor Test Measures in the Lab
A Proctor test measures how dense a soil becomes when it is compacted at different water contents. ASTM D698 describes this laboratory method. It produces a relationship between molding water content and dry unit weight, often drawn as a compaction curve.
The method uses a 5.50 lbf rammer dropped from a height of 12.0 inches (305 mm) into a mold 4 or 6 inches in diameter. ASTM D698 also notes that engineering fill, such as embankments, foundation pads and road bases, is compacted to a dense state.
How the Moisture-Density Curve Is Read
The highest point on the curve is the maximum dry density. The water content at that point is the optimum moisture. ODOT’s Supplement 1015 uses these same terms for its test.
Supplement 1015 names AASHTO T-99, Method C, as the moisture-density test ODOT uses. Item 203 accepts AASHTO T 99, AASHTO T 272 or Supplement 1015 for maximum dry density. ASTM D698 is a separate standard, and this article did not verify that the two test methods are equivalent.
What 95 Percent of Proctor Means in a Specification
A 95 percent Proctor specification compares the density measured in the field with the laboratory maximum dry density. Divide the field dry density by the maximum, then multiply by 100 to get the percentage.
ODOT Item 203.05 asks for the top 8 inches (200 mm) of the foundation to be compacted to 95 percent of maximum dry density. That number belongs to this clause of one state specification. It is not a universal rule, so read the test method the specification names.
Why the Required Percentage Changes by Job
The percentage depends on the part of the work and the method named for it. ODOT’s two documents use several figures, and the table lists each one this article verified.
| Clause | Edition | Percentage | Applies to |
|---|---|---|---|
| Item 203.05 | 2013 CMS | 95 percent | Top 8 inches (200 mm) of foundation, against maximum dry density |
| Item 203.07 B | 2013 CMS | 98 percent | Embankment, against maximum dry density from test section methods |
| Supplement 1015.05 | 2002 manual | 98 percent | Production area, against the test section maximum |
| Supplement 1015.07 | 2002 manual | 95 percent | Control section maximum, as 95 percent of the test section density |
Confirm the current edition before you cite either document. The 2013 CMS and the 2002 manual are different editions, and this article did not check whether either has been replaced.
Dry and wet density also differ by agency. ODOT and ASTM use dry density. A search summary says Caltrans uses wet density for relative compaction, which this article did not confirm from the Caltrans text.
Where the Compaction Calculator Fits
The Compaction Calculator answers a different question: how much compacted fill a loose volume makes. It uses swell and shrink factors for each soil type. It has no Proctor, density or percent-compaction input.
Subtracting shrink from the loose volume is a tempting shortcut, and it gives the wrong answer. For 100 loose cubic yards of common earth, the calculator gives 68.00 compacted cubic yards, not 85. The tool’s formula, compacted = loose x (1 – shrink) / (1 + swell), works in two steps:
- Convert to bank. Swell is 25 percent, so 100 / 1.25 = 80.00 cubic yards.
- Apply shrink. Shrink is 15 percent, so 80.00 x 0.85 = 68.00 cubic yards.
The same formula gives 59.26 cubic yards for clay (100 x 0.80 / 1.35) and 78.26 for sand or gravel (100 x 0.90 / 1.15). These are the tool’s planning factors, not sourced values. The tool page says figures vary with moisture and compaction.
Run the loose volume to compacted fill tool for the volume, then check a Proctor result for any density specification.
FAQs About Proctor Compaction
What does a Proctor test measure?
It measures the highest dry density a soil reaches in the lab, and the water content where that density occurs. That water content is called the optimum moisture.
Is 95 percent Proctor compaction a universal rule?
No. The 95 percent figure here comes from an Ohio highway specification, and it applies to a named part of that work. Check the percentage and test method in your own project specification.
Does the Compaction Calculator measure Proctor density?
No. It converts loose volume to compacted volume using swell and shrink factors for each soil type. It has no density or moisture input, and its page says it is not a substitute for a Proctor test.
Why do ODOT percentages differ between clauses?
Each clause names its own percentage and base. Item 203.05 uses 95 percent for the top 8 inches of foundation, while a 98 percent clause covers embankment work using test section methods.
Is ASTM D698 the same as AASHTO T-99 Method C?
The sources here do not confirm that they are equivalent. ODOT names AASHTO T-99, Method C, while ASTM D698 is a separate standard. Check which test method your specification cites.
Do Caltrans and ODOT measure density the same way?
This is not confirmed. ODOT and ASTM use dry density. A search summary says Caltrans uses wet density for relative compaction, but this article did not read the Caltrans method.
Which edition of the ODOT specification should I check?
Confirm the current edition with ODOT before you cite it. The 2013 CMS (Item 203) and the 2002 manual (Supplement 1015) are different editions, and this article did not verify which is current.
Sources and Further Reading
References Used in This Article
- ASTM International, ASTM D698-12(2021), store page (scope text), accessed 2026-11-12.
- Ohio Department of Transportation, Item 203, Roadway Excavation and Embankment (2013 CMS, state specification), accessed 2026-11-12.
The 95 percent figure here comes from a state highway specification, not a universal rule. Check the test method and percentage in your own project specification before you compact. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated 2026-11-12.
Shakeel Muzaffar is the Founder and Editor-in-Chief, with over 15 years of experience in digital publishing and online tool development. He oversees editorial quality and formula verification to ensure accurate, practical, and easy-to-use calculators.