Particle Size
The size of solid particles in the mud system is measured in microns. A micron(µ) is 1/1000 of a millimeter or 1/25400 of an inch. API classification of particle sizes is as below:
Particle Size, microns(μ) Particle Classification Sieve Size
Greater than 2000 Coarse 10
2000 to 250 Intermediate 60
250 to 74 Medium 200
74 to 44 Fine 325
44 to 2 Ultra-Fine 400
Less than 2 Colloidal –