Assuming your bike computer shows speed, here's how I figured my cadence out. Go to the website below and enter your chainring and cog info and print it out. Go for a ride and get in the gear that you normally cruise in and note your speed on the computer. Look up that gear ratio on the paper you printed out and find the speed you were going and that'll tell you your cadence. http://www.hostelshoppe.com/tech_gearcalc.php