How do I determine my body fat percentage?

Depends. There are several online tools for calculating bmi (http://www.Bmi-calculator.Net/body-fat-calculator/, http://www.Livestrong.Com/tools/body-fat-calculator/, http://www.Nhlbisupport.Com/bmi/) then, more accurately, a dietician or other trained profession can do a caliper measurement. There is a bioelectric impedence scale, and recently the usaf uses a "bod pod" to calculate body density and fat.