Adding and Subtracting Volumes

The human pyramid has always impressed audiences. Everyone from circus performers to high school cheerleaders knows that it is a show-stopping feat. Your cheerleading coach is dreaming of a human pyramid with $13$ levels (with each level containing $1$ less person than the level below it), and wants to put you in the middle position in the bottom row. If she succeeds, about how many time your own weight would you end up supporting?