Site investigation · Laboratory: soil classification
Hydrometer analysis calculator
Fine-fraction grading from hydrometer readings: particle diameter by Stokes' law and percent finer.
Standard: AS 1289.3.6.3 · Stokes' law · 152H hydrometer
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Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Dry soil mass | 50 | g |
| Gs | 2.68 | |
| Temperature | 22 | °C |
| t (min), corrected reading R (g/L) | 0.5, 44 1, 41 2, 37 4, 33 8, 29 15, 25 30, 21 60, 18 120, 15 240, 12 1440, 8 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Viscosity η at 22 °C | 0.955 | mPa·s |
| Gs correction a | 0.993 | |
| Largest D measured | 0.0563 | mm |
| % finer at first reading | 87.4 | % |
| Clay fraction (< 2 µm) | 19.5 | % |
| t = 0.5 min: D, % finer | 0.0563 mm, 87.4 % | |
| t = 1 min: D, % finer | 0.0408 mm, 81.4 % | |
| t = 2 min: D, % finer | 0.0299 mm, 73.5 % | |
| t = 4 min: D, % finer | 0.0218 mm, 65.6 % | |
| t = 8 min: D, % finer | 0.0159 mm, 57.6 % | |
| t = 15 min: D, % finer | 0.0119 mm, 49.7 % |
- ✓ Diameters decrease with time
Method, formulas and assumptions
- Effective depth L = 16.3 − 0.164R (cm) for a 152H hydrometer
- D = √[18ηL / ((Gs − 1)ρw g t)]
- % finer = R·a / Ms × 100, a = 1.65Gs / [2.65(Gs − 1)]
- Readings should already include meniscus, temperature and dispersant corrections
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.