Body fat percentage testing accuracy?

I have a scale that shows my body fat (not sure how it works) but it says 31. According to a height and weight chart I am also around 30-31 (which is fat.) I have a lot of muscle though, especially in my legs and I work out 5 times a week pretty vigorously so I always wondered if that fat reading was high. So, i had my personal trainer calculate my body fat with calipers and it came out at 21. I was shocked thats more than 30% less than the other readings. I'm 5'7" and 1/2" and weigh 180. Should I just get another test because so far the readings have ranged from "very good" to "overweight" I'd really like to know which reading is correct. Opinions please.

Public Comments

1. Calipers, when used correctly, are going to be much more accurate than one fo those $80 body fat scales. I've used one before and think they are way off most of the time. Check out www.bodybuilding.com for more info on calculations. Mike B http:www.bouma.ca
2. Those scales you're talking about usually show BMI (body mass index) and do NOT measure bodyfat. They give a "general" idea if you are overweight for your size, but you are correct in that they DON'T take into account how you are carrying that weight. For example, Zack Thomas, MLB for the Dolphins, is rock solid (I'd guess around 8 to 10% bodyfat) and is 5'-11" and 235 lbs. According to a BMI chart, he would be obese!! So stick to having your bodyfat measured...it's a surer sign of your health. Your PT should know how to measure your bodyfat properly, so stick with his/her results, and shoot for a bodyfat of between 10% to 12% for general good health.
3. The most accurate test you can get would be from a physician because when you do these tests online they dont measure the muscle in your body. When I take BMI tests online, I get a reading from overweight to obese, and I know that I'm not obese because I have a lot of muscle weight.
4. Many fitness trainers have the tools to do a body composition assessment that use several methods. This can include readings from Frame size BMI Hip to waist ratio Body Circumference measurements Skinfold calipers Bioelectrical impedance device (handheld or scale) And average of the readings will give you a good idea of where you are body fat percentage wise. Any reading that is significantly different from the others will usually be thrown out. There are also other ways of measuring body fat composition but are costly or not widely available. A couple of these are hydrostatic weighing and use of a bodpod. Also factors such as hydration/dehydration, time of day, and how recently you exercised will all have an effect on the readings. So long as you are doing the right type/amount of exercise and eating healthily you shouldn't worry too much about it. Do worry if you see a sudden increase/decrease in weight and don't have a reason for it. Then see a doctor.