A standard system of measurement for determining if a girls booty is in the correct size range. This is done by placing the tips of your thumbs together and pointing your pinkies straight out to determine if a females butt fits within that size range. This system of measurement can be misleading if you have been drinking and your calipers become more flexible leading to a morning of shame and self-loathing.
Situation 1:
Justin: "I was drinking too much last night and my butt calipers caused me to bring home a heffer."
Chris: "That's unfortunate, you should probably chalk this one up to a slump buster"
Situation 2:
Samer: "I saw this girl at the club last night and was so excited when she fit perfectly within my butt calipers. Unfortunately it turns out she was like sixty years old!"