# Porosity

Written by Jerry Ratzlaff on . Posted in Geotechnical Engineering

Porosity, abbreviated as n, a dimensionless number, is the ratio between the pore volume of a substance and its total volume.  Porosity of a measure of a rocks capacity to store fluids.

## Porosity formulas

 $$\large{ n = \frac {V_v} {V_t } }$$ $$\large{ n = \frac {V_v} {V_s \;+\; V_v } }$$ $$\large{ n = \frac { e } { 1 \;+\; e } }$$

### Where:

 Units English Metric $$\large{ n }$$ = porosity $$\large{dimensionless}$$ $$\large{ v }$$ = Darcy velocity or flux $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$ $$\large{ v_s }$$ = seepage velocity $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$ $$\large{ V_t }$$ = total volume of soil $$\large{ft^3}$$ $$\large{m^3}$$ $$\large{ e }$$ = void ratio $$\large{dimensionless}$$ $$\large{ V_s }$$ = volume of soil $$\large{ft^3}$$ $$\large{m^3}$$ $$\large{ V_v }$$ = volume of voids (air and water) $$\large{ft^3}$$ $$\large{m^3}$$

### Solve For:

 $$\large{ v_s = \frac{ v }{ n } }$$ $$\large{ v = v_s \; n }$$ $$\large{ V_t = \frac{ V_v }{ n } }$$ $$\large{ V_v = n \; V_t }$$

## Related Porosity formula

 $$\large{ n = \frac { v} { v_s} }$$ (seepage velocity)

### Where:

$$\large{ n }$$ = porosity

$$\large{ v }$$ = Darcy velocity or flux

$$\large{ v_s }$$ = seepage velocity