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Best smart scale for 2021: Withings, Fitbit, Garmin and Eufy, compared

The best smart scales can tell you about much more than just your weight.

Today's bathroom scales do a lot more than just weight measurement. Many have sensors that can estimate body metrics like your muscle mass and body fat, calculate your body mass index, measure your heart rate and even calculate your basal metabolic rate, all in an effort to keep track of your health, meet a fitness goal or help you lose weight.

Smart bathroom scales use Bluetooth or Wi-Fi to sync all of the body composition metrics they record about you to an app on your phone. Typically that's the app from the company that makes the scale, but in most cases, you can also sync that data to popular fitness apps like Google Fit or Apple Health, which can help you contextualize your body composition measurements but incorporating that data into existing information the apps have about your workout and dietary habits. Like we said, a Bluetooth smart scale does so much more than the bathroom scales of the past.

To make it easier for you to pick the best smart scale, let's go through the pros and cons of the top smart models on the market by Withings, Fitbit, Garmin and others.

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What makes the Eufy Smart Scale so great isn't just the scale itself -- it's the app that comes with it. The app, available for iOS and Android, is very easy to navigate and provides detailed data and reports of your weight, body fat, water, muscle mass, bone mass, BMI, BMR and more. The app will also flag those measurements as low, normal or high, so you know how your health stats compare to what's considered the standard in health and fitness for your height and age.

The Eufy scale supports up to 16 different users in the app. Simply select the correct user in the Eufy app and all of your data and metrics from the smart scale will sync to that profile in the mobile app. It also connects with the Apple Health app and Fitbit app.

James Martin/CNET

Withings' digital bathroom scale comes packed with lots of features that go above and beyond the rest. It provides detailed historical data and metrics on your weight, BMI, body fat, muscle mass, body water, heart rate and bone mass, so you can see how those measurements and your health and fitness change over weeks, months, quarters and years. This Withings scale also records the weather every day that you hop on the scale, to help you decide what to wear if you step on the smart scale first thing in the morning.

What sets the Body Cardio apart is that it has modes for pregnant women, babies and athletes, each tailored to specific needs. If you want the smart scale to track your pregnancy, it will plot your weight changes over the course of your pregnancy and suggest turning off the body composition features, which aren't as accurate while you're carrying.

Baby mode allows you to hold your infant and step on the smart scale to only measure their weight. Athlete mode accounts for professional athletes, bodybuilders and anyone who weighs more because they have a lot of muscle mass and low body fat and BMI.

Two more bonuses: This bathroom scale uses a rechargeable battery (with a battery life of approximately 18 months) -- many scales run on a bunch of AA batteries or AAA batteries -- and it supports up to eight different users.

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Garmin

Do you already use a Garmin fitness tracker? Then you might want to get a Garmin Index S2 to go with it. This scale is an update to the Index scale I originally tested in 2019. The Index S2 includes a new weight-tracking feature on the screen that keeps tabs on weight changes over the past 30 days of readings. 

The Garmin Connect app (Android and iOS) offers a holistic view of your health, including data and metrics such as your activity level, weight, BMI, body fat percentage and other measurements and data.

The smart scale measures weight, BMI, body fat, body water, muscle mass and bone mass, and it offers accurate charts to track weight loss and other data over a week, a month and a year. It uses four AA batteries, and battery life is up to nine months.

Fitbit

The Fitbit Aria Air is the latest smart scale from Fitbit and it measures weight, BMI and body fat. This digital bathroom scale is best for people who currently use a Fitbit wearable and want all of their data -- activity, nutrition, weight, BMI, body fat, sleep -- in one dashboard. 

The Aria Air is an update to the Aria 2 I tested last year. This Fitbit scale has a sleeker style and new screen. Like the Air 2, you can have multiple profiles for different family members, and each of their metrics and data are saved to their user profiles in the Fitbit app (Android and iOS).

The flaws in measuring body fat with a scale 

These smart scales all go way beyond the offerings of a typical digital scale. Each of them can measure your body composition, weight and body mass index, or BMI, using an electrical current that travels from the scale's sensor through your leg, across your pelvis and down the other leg. It measures how much resistance that current encounters and then uses a mathematical formula to estimate how much fat, muscle and bone makes up your entire weight.

While these features are useful, they aren't always reliable for sensing lean mass versus fat. Consumer Reports tested the accuracy of many scales that measure BMI and body fat percentage and found that most didn't hit the mark compared to a BodyPod -- one of the gold-standard clinical tests for body fat measurements.

Data inaccuracies when it comes to fat percentage can be chalked up to many things, including if you're sick, retaining water weight, have recently exercised, are menstruating or have consumed alcohol. One of the most influential factors is where you carry your weight -- if your chest and arms are slim, but you have more fat and muscle in your pelvis and legs, it might incorrectly calculate your overall body fat percentage.

Each smart scale I stepped on gave me a different body fat percentage, but each number was within a 10% range. But for muscle mass percentage measurements, the range was between 33% and 63%. Two of the scales I tested provide a basal metabolic rate, but there was a whopping 631-calorie difference between the two. That's more than one McDonald's Big Mac or three glazed Krispy Kreme donuts.

It's also worth mentioning that BMI is not considered an accurate measure of one's body fat or overall fitness, so even correct BMI information should be taken with a grain of salt.

All of this is to say, don't get caught up in those metrics. Follow the directions that come with your smart scale to get the most accurate measurements and data possible, and if you're concerned about your body fat percentage, body composition, health or fitness, talk to your doctor about getting a proper scan. All the models on this best smart scale list give accurate readings when it comes to body weight -- which is the most important factor when you're focused on weight loss. We'll update this list periodically.

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The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.