Are these online body fat percentage calculators accurate?

I went on a body fat calculator and it told me to measure my waist and stuff. So I did and It told me I had a % of 20! I find it hard to believe when I am 15, a boy and weigh 148 pounds. Should I trust these calculators, or are they inaccurate? thanks.

Public Comments

1. Tell me what website and I'll do mine and see if its correct.
2. Without calipers or testing you in person, I have no idea how these people even get off saying that it's valid in any way! For instance what if you're a totally muscle-bound man?