The image above represents dimensionless radius.

To compute for the dimensionless radius, two essential parameters are needed and these parameters are **external radius (r _{e}) and well radius (r_{w}).**

The formula for calculating the dimensionless radius:

r_{D} = ^{re} / _{r}_{w}

Where;

r_{D} = Dimensionless Radius

r_{e} = External Radius

r_{w} = Well Radius

Let’s solve an example;

Given that the external radius is 18 and the well radius is 16.

Find the dimensionless radius?

This implies that;

r_{e} = External Radius = 18

r_{w} = Well Radius = 16

r_{D} = ^{re} / _{r}_{w}

r_{D} = ^{18} / _{16}

r_{D} = 1.125

Therefore, the **dimensionless radius **is **1.125.**

**Calculating for the External Radius when the Dimensionless Radius and the Well Radius is Given.**

r_{e} = r_{D} x r_{w}

Where;

r_{e} = External Radius

r_{D} = Dimensionless Radius

r_{w} = Well Radius

Let’s solve an example;

Given that the dimensionless radius is 9 and the well radius is 20.

Find the external radius?

This implies that;

r_{D} = Dimensionless Radius = 9

r_{w} = Well Radius = 20

r_{e} = r_{D} x r_{w}

r_{e} = 9 x 20

r_{e} = 180

Therefore, the **external radius **is **180.**