Body-fat scales send an electrical pulse through the body to gauge body weight/density. Many body-fat scales display both body-fat percentage and body mass index (BMI), a rough estimate of body composition calculated using a person's height and weight. According to the Centers for Disease Control and Prevention, BMI can be useful for determining whether a person is overweight, but it's not foolproof.
For example, athletes with a great deal of muscle may have a high BMI reading even though they don't possess a lot of body fat. Similarly, body-fat percentages look at how much of a person's body is composed of fat. While both of these calculations can be useful, experts caution that they do not provide a complete picture of an individual's health. Experts say an individual's waist circumference, hip-to-waist ratio, blood pressure and cholesterol levels are also important indicators of health.
Body-fat scales tend to be off by as much as 5 to 10 percent. Muscle & Fitness Hers magazine consults Dr. Richard Pierson Jr., professor of clinical medicine at St. Luke's-Roosevelt Hospital of Columbia University, on a number of body-fat measurement methods. He acknowledges that individual readings may not be accurate, but points out that body-fat scales are a good way to monitor changes in body fat over short periods of time.
Scale readings can be thrown off by a number of factors, such as how much water you drink, whether you have a full bladder or if you have foot calluses. Cedric Bryant, chief science officer for the American Council on Exercise, tells WebMD that body-fat scales should be used under similar conditions each time, such as time of day and fluid and food intake, noting that even a woman's menstrual cycle can affect readings. "However, with all this factored in, these scales are an easy, at-home way to keep track of your weight and fat-loss progress," says Bryant.
High-tech body-fat scales link with a remote application using a Wi-Fi connection. They're more expensive than digital scales but can be more affordable than standard body-fat scales. For example, the Fitbit Aria Wi-Fi Smart Scale (Est. $130) is one of the least expensive high-tech body-fat scales yet offers more functionality than most.
The Fitbit Aria connects remotely to the Fitbit website, which offers a robust selection of fitness and weight-management tools for tracking progress over time. The scale can be configured to track up to eight different users, each of whom have their own profile on the Fitbit website and their own personal measurements and goals. In addition to tracking weight and body composition, users can enter their daily activities and food intake on the website, which then calculates caloric values based on information in its database. Users can also connect with other Fitbit members to offer encouragement toward achieving their goals. Further motivation is offered by the interface itself, which rewards users with badges for every 5 pounds lost and offers encouraging messages and recommendations.
The biggest downside to the scale is that some users have difficulty configuring the scale and the Wi-Fi connection, but others say setup is a cinch. Nearly all Fitbit consumers agree both the scale and the cloud-based application are intuitive to use after initial setup.
Another option among high-tech body-fat scales is the Withings WS-50 Smart Body Analyzer (Est. $150). It's a bit more expensive than the Fitbit, but most users say setup is easy and intuitive. Like the Fitbit, the Withings can be configured to track statistics of up to eight users, and it tracks your progress in easy-to-read graphs and tables, making weight loss feel more like a game. It has a higher, 396-pound weight capacity compared to the Aria's 350-pound maximum.
An already popular manufacturer of digital bathroom scales, EatSmart recently made its foray into the body-fat scale scene with its EatSmart Precision GetFit Digital Body Fat Scale (Est. $54), a considerably more affordable body-fat scale compared to others.
The Wirecutter names the Withings WS-50 as its best smart scale because of its superior features: Unlike the Fitbit Aria, it has the ability to track your resting heart rate and even monitor the air quality of your surroundings. With these extra functionalities in mind, we chose the Withings WS-50 as our top pick for body-fat scales.