Find the lowest note in your overall range. Using a piano, start on middle C if you are a female; if you are male, start five notes lower on F. Write down the lowest singable note in your range.
Sing in half steps starting on your lowest note. When you notice a change in the quality of your voice when you sing a specific note, write down that note. All vocalists have passagios—the change in your vocal register—in different places in their voices. Singers have several passagios.
Ascend through the remaining portion of your range, taking note every time you feel a change in your register. A passagio should occur between the low and middle ranges, the middle and high ranges and the high and extreme ranges.