Try this google chrome trick.
You know the address bar or URL bar (also called as Omnibox in Chrome) in the Chrome browser.
You use it to enter some URL or keyword you want to search. Perfect. No Issues.
But, did you know that you can also perform calculations or conversions directly in the Omnibox.
Just go to chrome, and type 300+5 in the URL bar and see the result. Also try typing:
2 miles in km
Here is the screenshot from my machine.
Enjoy your new calculator and conversion tool.