The other day at work looking up air density conversions I came across a great resource called the Omni Calculator, it can convert and calculate all kinds of stuff. https://www.omnicalculator.com

Click on the 3 lines to access the different options on the desk top version, mobile has a search bar and topics on the home page

For the air density conversion here is the exact page https://www.omnicalculator.com/physics/air-density