Want to shed some fat? “Ditch your scale” is oft-repeated advice from fitness pros. No matter how accurate, they say, a scale only tells you how much you weigh—it says nothing about what that weight consists of.

If you’re a 6’2”, 225-pound man, for example, you could be a well-fed couch potato or you could be Arnold Schwarzenegger on the Mr. Olympia stage in 1974. The couch potato would be overweight and likely prediabetic. His cardiovascular conditioning would be next to nil, and his strength not much better. The other guy would be, well, Mr. Olympia.

The lesson: The scale doesn’t mean much.

What does matter—whether you’re seeking improved health, a better physique, or both—is what you’re made of: how much of you is muscle, bone, skin, and other lean tissue, and how much is fat? And more importantly, how are those numbers changing over time?

To find that crucial information out, you need a body composition test—a tool that indirectly estimates body fat and lean tissue (the only direct way to measure these things is dissection, which we don’t recommend).

Right now, there are numerous such tools available. Here’s our breakdown of the pros and cons of each one:

muscular abs

How to Determine Your Ideal Body Fat Percentage

When it comes to body composition, knowledge is power.

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