Sediment Particle Size Classifier (Wentworth Scale)
Classify sediment by the Wentworth scale from diameter in mm or micrometers.
Returns phi (φ) value, class from clay to boulders, and Stokes settling velocity.
Wentworth Scale A standard classification system for sediment grain size, ranging from clay (<0.0039 mm) to boulder (>256 mm). Developed by Chester Wentworth in 1922 and still the global standard in sedimentology.
Phi (φ) Scale φ = −log₂(d), where d is diameter in millimetres. The phi scale is logarithmic — each whole unit represents a doubling of grain size. Coarser grains have negative phi values.
Stokes Settling Velocity For fine particles (clay to fine sand), settling velocity in still water: vs = (ρs − ρf) × g × d² / (18 × μ) Using quartz density (2650 kg/m³), water at 20°C (μ = 0.001 Pa·s).