What is the Wentworth scale?

The Wentworth scale (1922) is a standard grain-size classification system for sedimentary particles. It divides sediment into named classes — from clay ( 256 mm) — each separated by a factor of 2.

What is the phi (φ) scale?

The phi scale is a logarithmic transformation of grain diameter: φ = −log₂(d in mm). Finer particles have higher (more positive) phi values; coarser particles have negative phi values. It linearizes the wide range of sediment sizes for statistical analysis.

How accurate is the classification?

The classification follows the standard Wentworth boundaries exactly. Accuracy depends on how precisely you measure the actual grain diameter — field estimates from a hand lens are less precise than laser diffraction or sieve analysis.

What units can I enter?

You can enter the diameter in millimeters (mm) or micrometers (µm). Micrometers are convenient for fine-grained sediments like clay and silt, while millimeters suit sand, gravel, and coarser material.

What is the difference between silt and clay?

By the Wentworth scale, clay particles are smaller than 0.002 mm (2 µm), while silt ranges from 0.002 mm to 0.0625 mm. Clays also differ mineralogically — they are typically phyllosilicate minerals — but size alone defines the Wentworth boundary.

Sediment Size Classifier

Name: Sediment Size Classifier
Availability: InStock
Author: Nham Vu

Enter a particle diameter to instantly classify it on the Wentworth grain-size scale (clay through boulders).

Grain Diameter

Diameter (mm)

Quick Examples

Enter a grain diameter to see the classification

Wentworth Scale Reference

Class	Sub-class	Min (mm)	Max (mm)	φ range

Summary

Enter a particle diameter to instantly classify it on the Wentworth grain-size scale (clay through boulders).

How it works

Enter the particle diameter in mm or switch to micrometers (µm).
The tool converts the value to millimeters and computes the phi (φ) value using φ = −log₂(d).
The diameter is compared against the Wentworth scale boundaries to identify the class.
Results show the class name, sub-class, phi range, and a visual position on the full scale.
Use the reference table below the result to explore all 14 Wentworth classes at a glance.

Use cases

Classify sediment samples collected during field geology surveys.
Verify grain-size measurements from sieve analysis in a lab.
Teach Wentworth scale concepts in earth science or sedimentology courses.
Cross-check sediment descriptions in geotechnical or environmental reports.
Quickly convert between phi scale and physical diameter for research.
Identify sediment type in coastal or river-bed studies.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu