From stepping on a scale every day to keeping a close eye on the fit of your jeans, there are many ways to assess how healthy your weight and size are. And the discussion about whether body mass index (BMI) or waist circumference or something entirely different is best continues, most recently reignited when this season's Biggest Loser winner Rachel Fredrickson won with an alarmingly low BMI of 18 at 105 pounds.

Clear up the confusion and learn the latest on the benefits and drawbacks of the three most popular measurements to determine which is best for you.

Body Mass Index

The BMI is a standardized formula to determine the ratio between height and weight. BMI has been shown to be a fairly reliable indicator of body fat for most adults, though not for the elderly or those with a lot of muscle tone. "Healthy" BMI is considered to be from 19 to 25. Calculate yours here.

Best used for: "Body mass index is a quick way to categorize someone as underweight, normal weight, overweight, or obese," says Mary Hartley, R.D., nutrition expert for

Scale Weight

A lot of people have very complicated relationships with the scale. Weight fluctuates naturally by a few pounds all the time based on a variety of factors including stress, hydration, menstruation, and even time of day, so daily weigh-ins can often fuel frustration and self-criticism instead of empowerment. [Tweet this!]

Best used for: Weekly or monthly check-ins for overall health and disease risk.

Waist Circumference

It doesn't make sense to take a tape measure to your stomach more than every four to six weeks, and Hartley says every six months to one year is optimal. "Take measurements correctly, whether using a scale, measuring tape, calipers, or a sophisticated tech device," she recommends. Your ideal waist size should be no more that half your height. For example, a five-foot-four-inch female should have a waist size of no more than 32 inches.

Best used for: Tracking changes during lifestyle modifications. Hitting the gym for some extra cardio and core work? Measurements every few months will be a great way to check your progress.

The Bottom Line

Knowing your numbers is an important first step in evaluating your health status and potential health risks, but ultimately there is no such thing as perfect numbers. Trust your body to find your own healthy set point with a balanced lifestyle of nutrition, physical activity (like strength training without weights), and positive relationships with others and yourself.

If taking measurements produces anxiety, negative judgments, or even depression, it's obviously not beneficial. And "a continuous desire to obsessively check measurements may indicate a mental health problem," Hartley says. You are worth so much more than the size of your jeans!

By Katie McGrath for