This is how a SWAG average power on a bike ride:http://ns1.omnitech.net/cycle/
My assumptions, recently updated, are:
* 86F, 600' elevation, 30% humidity, and 1 atmosphere of pressure
* 25% human efficiency (racers might be a little more, newbies a little less)
* 95% bike efficiency (Rusty bearings and flat tires would be less, race-bike better)
* 0.004 Coefficient of Rolling Resistance (Recently adjusted - on the low side for road, just to be fair).
* 0.6 Coefficient of Wind Resistance (on the drops, relatively upright, larger mass)
* 1.1 m^2 frontal surface area (I'm a big guy)
* One stop every mile (Roughly what I do in Irving).
There are such huge variances in some of these based on intarwebs scientific abstracts that I'm not even sure if this is valid. Whenever I get a power meter, I'll tweak this to be more accurate. I may get a couple different sized people to ride my bike for comparison. That won't show any of the Coefficients of Friction directly, nor human or bike efficiencies, or any of these numbers.
There are plenty of other tools out there, such as:http://www.analyticcycling.com/ForcesPower_Page.htmlhttp://omnitech.net/xaminmo/2014/06/19/bicycle-energy-calculator-2/