Density is defined as the density of the atmosphere. This is calculated using the molecular weight, pressure and temperature. This is in turn used to calculate the drag on the spacecraft.
To calculate a density please modify any of the formboxes and click on the calculate density button.
The density link will reload this page in the browser so that the current parameters can be bookmarked.
This script is under the GPL license which basically welcomes you to copy or modify this and allows anyone else to copy or modify your version if you make it public.