Sometimes, we don't have the luxury of having a phone, watch or clock nearby to keep track of time. Fortunately, many of us already have other methods to accurate measure elapsed time in our arsenal without even knowing it. Since most people have a few songs that they know very well, they can use those songs to keep track of chunks of time.
Interestingly enough, most people use music to keep track of time in situations regarding health. Washinghands.net recommends children to sing "Row, Row, Row Your Boat" twice to ensure that they wash their hands enough. Music can also be used to measure how long you've been running or doing push-ups while giving you a mental boost to get through the sweaty workout.
A small sample study by the University of Illinois College of Medicine found that people that used the tune "Stayin' Alive" to administer the CPR technique maintained an ideal 103 bpm (beats per minute) pulse and could retain their skills better weeks after their training.
All you need is a song you can't forget and can reproduce consistently in your mind (or out loud!) and a knowledge of how long the song—or a portion of it—takes, if you want to keep track of elapsed time. If you want to match a specific pace, such as 30 sit-ups a minute, find a song with a multiple or factor of the pace, preferably and usually by 2 or 4, and use that song as your mental engine. Those of you wanting to figure out the pace of a song can use the tap feature of a metronome to measure the bpm.
This is where I would brag about running 8 miles in the length of Sgt. Pepper's Lonely Hearts Club Band, but in reality it'd probably take me at least the length of the Echochrome 2 soundtrack. Oh, and don't choose 4'33" as your go-to song; if it works for you, you're a human clock and don't need this lifehack at all.