there's this wonderful new invention called "google." took me less than 10 seconds to find this
by searching "video aspect ratio chart." Forgive the snarkiness, but being able to research this by yourself is an important skill to have. Wikipedia is a great place to start looking
Here's the relevant quote "16:9 (1.77:1) (generally named as "Sixteen-Nine", "Sixteen-by-Nine" and "Sixteen-to-Nine") is the international standard format of HDTV,"
So what are your sequence settings? If you're material was shot within the last few years, it's almost definitely 16:9 (also known as 1.77:1).