How Accurate are Fitness Trackers? A Comparative Analysis of Garmin, Apple, Fitbit, and Withings

Kathleen Zhang
Kathleen Zhang
July 10, 2023 · 3 min read Sources Verified
Ketut Subiyanto // Pexels

How accurate are fitness trackers?

Today, keeping track of your health is more within reach than ever with the widespread distribution and use of fitness trackers alike. But how accurate is your device? Are you really getting those 10k steps a day, or did you really burn that many calories in your morning 5K run? This article is aimed at exploring the accuracy of the watches produced by the following four leading fitness tracker companies: Garmin, Apple, Fitbit, and Withings. In doing so, we hope to understand how reliable the data from wearable devices is and how effectively they can be used to monitor health behaviors.

Please note that the compilation of data will solely rely on information published in peer-reviewed journals. This is due to the fact that manufacturers are not legally obligated to disclose accuracy testing unless their products are classified as medical devices.

If you are still experiencing decision fatigue when it comes to choosing your device, check out this article to help you narrow down your selection.

How accurate is my Garmin watch?

In a comprehensive review of 32 studies, Garmin activity trackers demonstrated higher accuracy in tracking steps but limited studies were available for assessing speed, elevation, and sleep tracking. Furthermore, the accuracy of distance, energy expenditure, and heart rate (HR) tracking was found to be comparatively lower.

Accurately tracks: Steps

Inaccurately tracks: Energy expenditure, distance, heart rate, and sleep

How accurate is my Apple Watch?

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Research shows the Apple Watch to be highly accurate when measuring daily step counts, particularly at a moderate intensity level. However, this preciseness fluctuated with the device overestimating at slower walking speeds and underestimating at faster ones. While no formal research has been shared discussing HR and energy expenditure in normal patients, one study conducted involving patients with cardiovascular disease found the Apple Watch heart rate during exercise to be accurate, suggesting its potential use in HR-guided training programs for cardiac rehabilitation. However, the device consistently overestimates energy expenditure in this patient population.

Accurately tracks: Heart rate and steps

Inaccurately tracks: Energy expenditure

How accurate is my Fitbit device?

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A review of 67 studies examining Fitbit devices highlighted variations in their accuracy for step counting. During controlled testing (ie. on a treadmill), Fitbit devices tended to underestimate steps, whereas in real-life scenarios, they tended to overestimate steps. Notably, Fitbit devices showed more precise step counts when placed on the torso during normal walking, while for slow walking this was extended to placement on the wrist during jogging and on the ankle. However, the measurement of energy expenditure was generally found to be inaccurate. Fitbit devices demonstrated similar results to research-grade accelerometers in measuring time spent in bed and time sleeping but exhibited an inclination to overestimate higher-intensity activities and underestimate distance during faster-paced walking.

Accurately tracks: Sleep and steps

Inaccurately tracks: Energy expenditure and distance

How accurate is my Withings ScanWatch?

A recent study demonstrated a strong correlation between estimated steps from the Withings and those obtained using devices widely considered as gold standards for step and activity estimation. Additionally, the Withings tended to assess relative energy expenditure levels with exceptional accuracy. Likewise, recent research suggests that while the Withings showed acceptable accuracy in measuring HR for general consumer use, it may not be suitable for situations requiring more precise HR measurements, such as healthcare or clinical trials. Notably, the Withings displayed lower accuracy in measuring HR during mobile activities like walking, gardening, and household tasks, compared to more sedentary activities such as desk work, eating or drinking, and sitting.

Accurately tracks: Energy expenditure, heart rate (sedentary), and steps

Inaccurately tracks: Heart rate (mobile)

So we’ve come back to the age-old question. How accurate are fitness trackers?

In short, they’re not. The compilation of research further pushes for the narrative that we should treat these fitness trackers as tools to give us relative information about our overall health. Rather than focusing too deeply on the individual metrics, we should zoom out and focus on the general trends.

Health applications like Guava, can help you visualize and identify patterns in the information your device is tracking around the clock, ultimately supporting you in making more informed health decisions. Even if you switch devices, Guava can help you see all of your data together in one place.

While this may not have been the answer you wanted to hear, have no fear! This doesn’t mean you should stop aiming to hit your daily 10,000 steps or disregard the metrics entirely. This information just suggests that it is advisable to avoid basing lifestyle and your health decisions solely on these numerical values. Though, I’m definitely still guilty of walking in laps around my home until my watch buzzes when I hit that magical number.

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