>>1605584FTP is your maximal average power over an hour interval, but most people find it easier to ride for 20 minutes and say the FTP is .95 of that. If you have access to a stationary bike with a power meter, that's the easiest and most accurate way to test yourself.
Otherwise, ride an uninterrupted uphill climb for 20 minutes, and keep track of where you started and stopped. Figure out the elevation gain over the course, and enter the details into
http://www.u.arizona.edu/~sandiway/bike/climb.html.
Optionally, you can use software to do this estimation automatically if you can record the ride with a gps app on your phone. Strava does this automatically for specific segments, but if you want second-by-second estimated power numbers, you can put ride data into goldencheetah to generate an estimated power profile.
