Because people and computers speak different number languages, it is often necessary to convert numbers from one system to another. The easiest way to perform the conversion is with a scientific calculator. However, there will be cases for which you need to perform the conversion by hand.
If you don't have a scientific calculator, the Windows Calculator program is a reasonable facsimile. Open it, go to the View menu, and change the setting from Standard to Scientific. Click the button next to a numbering system. Then enter a number, and if you click a button next to a different numbering type, the number will be converted for you. There are similar tools for UNIX and Mac OS.