THIS POST IS SUPER OLD…I’VE SINCE UPDATE THIS A WHOLE LOT: https://synergisticsinging.com/how-to-find-your-vocal-range-on-piano/

To know the right exercises to improve your singing, you have to know your voice, first. Here is one way to do that! Although there are multiple “ranges” in your voice (volume, pitch, color, vowel, etc.) pitch is an easy place to start. Here’s a quick video guide for guys on finding your most comfortable pitches to sing in, even if you don’t have access to a piano.