Asta is right, a punch and the power in a punch come from the correct stance and then technique and speed/power of hip rotation, shoulder thrust and correct delivery of fist.

To show you the power of a punch, Georges St. Pierre, an MMA fighter who is 5’10 and weighs 170 lbs.
 
- Georges St. Pierre's punch registers at 2859 lbs of force
- Georges St. Pierre's kick registers at 3477 lbs of force
- Georges St. Pierre's punch/kick combo registers at 6000+ lbs of force in under 1 second
- Speed: Georges St. Pierre's takedown generates 2400 watts of power in 1.17 second (on par with Rashad Evans) 
- Georges St. Pierre's superman punch moves at 15 feet/second (twice as fast as his normal punch)

from [url=http://www.bloodyelbow.com/2011/4/29/2142021/sport-science-georges-st-pierres-punching-power-2859-lbs-of-force] sports science [/url]