Body fat calculators that only use your weight and height are calculating BMI (Body Mass Index) not body fat per say. The vast majority of electronic scales that claim to measure body fat are actually measuring BMI. This number will always be a lot higher than your actual body fat percentage.
My particular bodyfat is actually around 10%, but my BMI shows up at 21%.
The calculator you found above only uses height, weight, and waist size, which also isn't an accurate way to measure body fat, especially for a body builder. Muscle is more dense than fat, so a 6' tall, highly active athelete, weighing 190 pounds, with a 32 inch waist is going to weigh more than an equivilent weight & height person who is sedentary.
If you don't want to do the water tank or caliper test. Your best bet is to find calculators that include some or all the measurements for hips, wrist, neck size, and also include a rating for your athleticism.
Here's one I quickly found that at least includes wrist size and your athletic rating:
http://www.zoneperfect.com/Site/content/Calculator_Men.asp
And here's another:
http://www.motivationstation.net/bodyfat.htm
Try those on for size...
Please Scroll Down to See Forums Below 
