A simple body fat calculator.
All you need to enter is your waist in inches and your weight in pounds.
There are more accurate methods. However this method is good enough to get you started.
If you want the most accurate reading an underwater test
Hand calipers are accurate in the hands of the right person. Using them properly takes skill
cm to inches – cm x 2.54 = inches
Kg to lb – kilograms x 2.2 = pounds