How do you measure power output?

Road Red

I read a lot about power output, whats needed for climbs etc.

How is it measured?

phil s

With a powermeter. Powertap are probably the most commonly used among amateurs, SRMs more prevalent amongst the pros. Powertap is hub based, SRM is crank-based.

sub55

https://www.srm.de/store/product_info.php?info=p5_SRM-Wireless-Training-System---DuraAce-Standard.html about 3,500 euro
or you can hire them http://www.cyclepowermeters.com/

Alex_Simmons/RST

See here for a brief intro:

http://en.wikipedia.org/wiki/Cycling_power_meter

lots of info here as well:

http://www.trainwithpower.net/