Turns out some people are pretty out of touch when it comes to their weight. A new Gallup survey shows only 36% of Americans think they're overweight. That's not even close to the 69% of adults in the U.S. who actually are overweight or obese, according to the Centers for Disease Control and Prevention. Talk about a reality check.

And this isn't the first time Americans have guessed wrong: A review of 69 studies published in the journal Pediatrics found that nearly 51% of parents with overweight or obese children underestimated their kid's weight. The researchers in that study said it's likely that prevalence of overweight kids skewed the parents' perceptions of what's normal.

All the more reason to learn what it really means to be overweight and obese. A quick way to figure it out is to calculate your Body Mass Index (BMI). It's a measure of body fat that factors in your height and weight. A BMI of 25 or more will put you into the overweight category, while a score above 30 means you're in obese territory. A normal BMI is between 18.5 and 24.9.

While BMI is easy to calculate, it does have its limitations. For one, it may overestimate body fat in athletes or anyone with a muscular build.

Though BMI isn't a perfect measure, it's still a good place to start if you're unsure of where you stand.

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