Proctor Compaction Curve Helper
Convert a field wet (bulk) density and moisture content into dry density, and compare it against the Proctor maximum dry density to get relative compaction. It is the quick check earthworks crews and testers use to see whether a compacted layer passes a density specification.
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Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the wet (bulk) density measured in the field (e.g. by nuclear density gauge or sand replacement) in t/m³.
- Enter the moisture content of the material as a percentage.
- Optionally enter the maximum dry density from your standard or modified Proctor test to get the relative compaction percentage.
How it works
Wet density includes the mass of water, so the dry density is found by removing the moisture: dry = wet / (1 + moisture/100). The relative compaction is the field dry density expressed as a percentage of the Proctor maximum dry density (dry / max dry × 100). Comparing the field dry density and moisture against the laboratory Proctor curve tells you whether the layer was compacted well enough and near enough to optimum moisture.
Worked example
Worked example. A layer tests at a wet density of 2.1 t/m³ and 12% moisture: dry density = 2.1 / (1 + 12/100) = 2.1 / 1.12 = 1.875 t/m³. Against a Proctor maximum dry density of 1.95 t/m³ the relative compaction is 1.875 / 1.95 × 100 = 96.15%, which passes a typical ≥ 95% specification.
Common mistakes
- Comparing the wet density (not the dry density) against the Proctor maximum — always convert to dry density first.
- Mixing units: enter densities in t/m³ consistently (2.1 t/m³, not 2100 kg/m³).
- Forgetting that passing density near-optimum moisture matters — high compaction well off optimum can still be a problem.
Frequently asked questions
What relative compaction do I need?
It depends on the specification, but ≥ 95% of the standard (or modified) Proctor maximum dry density near optimum moisture is common for structural fill and subgrade.
Do I need the maximum dry density?
No — leave it blank and you still get the dry density. Add the Proctor maximum dry density when you want the relative compaction percentage.
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Cite this tool
Zerdly. (2026). Proctor Compaction Curve Helper. Retrieved from https://www.zerdly.com/tools/proctor-compaction-curve-helper/
Tip: Enter any known values to calculate the remaining results.
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