Earth Science & Energy
Beach Sand Grain Settling Fall Velocity (Rubey Equation) Sizer
Calculate beach sand grain settling fall velocity (rubey equation) using the stated engineering or scientific relationship and adjustable field inputs.
Preparing your result…
What this calculator does
Calculates Beach Sand Grain Settling Fall Velocity (Rubey Equation) Sizer using the formula verified against the cited source.
What your result means
An estimate from the inputs you enter, within the scope stated below — not advice.
Formula
w = [√(2/3+36ν²/(gD³R))−√(36ν²/(gD³R))]√(gD³R)/D
The step-by-step working for your own numbers appears with the result above and in the PDF report.
Frequently asked questions
Symbols and assumptions
- Inputs
- The values entered in the fields above
- • Rubey fall speed w=[√(2/3+36ν²/(gD³R))−√(36ν²/(gD³R))]√(gDR), R=grain specific gravity−1. D m, ν m²/s, g m/s² give w m/s.
Sources and review
Reviewed 2026-10-18 · Next review 2027-04-18
- • The original √(gD³R)/D is algebraically equivalent for D>0. Require submerged relative density R>0 and positive viscosity/diameter. This is still-fluid settling for the empirical grain assumptions, not turbulent suspension or beach transport; shape and size-range accuracy matter.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
Quick reference
| Scenario | Grain diameter (mm) | Grain specific gravity | Water kinematic viscosity (mm²/s) | Settling velocity |
|---|---|---|---|---|
| Worked example | 0.5 | 2.65 | 1.004 | 0.0624 m/s |
| Half the amounts | 0.25 | 1.33 | 0.502 | 0.0141 m/s |
| Double the amounts | 1 | 5.3 | 2.008 | 0.1561 m/s |
Need the full picture? Get the detailed PDF report with charts, tables, formulas and working steps.
Reviewed 2026-10-18 · Next review 2027-04-18
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