# Uniformity Coefficient

Written by Jerry Ratzlaff on . Posted in Geotechnical Engineering

Uniformity coefficient, abbreviated as $$C_u$$, also called coefficient of uniformity, a dimensionless number, classifies a soil as well graded or poorly graded. For the soil to be well graded for a given sample, the range must be between greater than 4 to 6.  If less than 4 it is classified as poorly graded.

## Uniformity Coefficient formula

 $$\large{ C_u = \frac{ D_{60} }{ D_{10} } }$$

### Where:

 Units English Metric $$\large{ C_u }$$ = uniformity coefficient $$\large{dimensionless}$$ $$\large{ D_{10} }$$ = is the sieve diameter (grain size) which there are 10% of particles go through. $$\large{in}$$ $$\large{mm}$$ $$\large{ D_{60} }$$ = is the sieve diameter (grain size) which there are 60% of particles go through. $$\large{in}$$ $$\large{mm}$$