Reviews You Can Rely On

How We Tested GPS Sports Watches

By Amber King ⋅ Senior Review Editor
Monday August 16, 2021

To see how these products tracked our athletes' movements, we covered some ground. We logged thousands of miles, mainly on foot but also while biking and swimming. Whether our feet were in running shoes, mountaineering boots, or barefoot on the beach, our testing was real-world and comparative. We would regularly wear and compare multiple watches on the same endeavor, but we also wore each one alone to focus our full attention on it.

Our team of diverse testers captured different perspectives on what makes an outstanding GPS watch. Our lead tester logged fifteen to twenty training hours a week and monitored virtually every one of her training and active hours with one or more of the products in this review.

After this much use, we are experts on these watches and are excited to share the details with you.

Navigating the foggy ridges of the Faroe Islands can be dangerous...
Navigating the foggy ridges of the Faroe Islands can be dangerous, but with a GPS watch with navigation in tow, we felt a little more confident.
Photo: Amber King


The absolute main discerning category that affects watch price is the number of features. We compared each product to a list of potential features. This list combines features included in each watch's hardware, software, and user platforms on your computer or an associated app. Some devices can be customized further. The list of potential features we compared are timekeeping, GPS distance and speed, GPS data recording, GPS navigation, step count, sleep tracking, built-in heart rate, compatibility with external sensors, dynamics, metrics, barometer, altimeter, thermometer, smartwatch functions, and more.

Usually, it can be assumed that an increase in features directly affects all other variables in our tests. Sometimes the effect is positive; for example, some added features that pertain to metrics collection will enhance the accuracy. However, sometimes additional features would lower our scores. A good example of this is when there are so many features that the watch becomes difficult to use or requires a lot of time investment to learn how to use it.

The Garmin Fenix 6 Pro comes with several preloaded maps that will...
The Garmin Fenix 6 Pro comes with several preloaded maps that will show your current position so you don't get lost when daydreaming down the dirt road.
Photo: Amber King

Battery Life

Battery Life is mostly important to endurance athletes, but it can also be frustrating to recharge your watch every day, even as a recreational athlete. A number of variables make it challenging to test the battery life of these GPS watches fairly because it hinges on how you use your watch. There are two battery usage types that are important — normal use and activity usage. We tested normal use (some manufacturers call this "smartwatch usage") to find out how many days each watch stays charged when we run only a few hours a week and use it as a daily smartwatch, which included fielding random numbers of text notifications a day.

We tested activity usage to determine how many hours each watch can last during a nonstop activity, like a race. To do this, we let each watch run tracking data from a full charge until it was empty to see which watch would make your 100-mile ultra without needing a charge and which wouldn't. An ultra runner, cyclist, or triathlete might need the battery to last during their activity for 10+ hours.

One of our past tests took us through the streets of Frankfurt...
One of our past tests took us through the streets of Frankfurt, Germany in the Frankfurt Marathon.
Photo: Larin McPeak

Ease of Use

This category is absolutely essential to any GPS watch purchase. It measures the watches' capacity to meet its intended purpose intuitively and straightforwardly. Sometimes one flaw can ruin the interaction and prevent the user from successfully acquiring necessary data. This category also includes how the watches interact with their software platforms, whether that be an app, a website, or a program (or all three). If the syncing, data sharing, and data presentation on the platform is difficult to operate, view, or understand, then even if the watch is amazing, the user experience can be frustrating or ruined.

By simply using the devices and sharing them with a diverse test team, we developed and distilled a significant body of user experience. We back up our opinions with years of experience and months of testing.

We tested the buttons and how easily we could see the screen in both...
We tested the buttons and how easily we could see the screen in both high and low light conditions. Buttons on the Garmin 45S could be used with either thick or thin gloves during this short ski tour.
Photo: Amber King


If a watch is inaccurate, the data is skewed, and the product is not completing its designed task. That said, no watch can be perfect. There are just too many variables to consider. To evaluate this metric, we had to repeat a lot of our test runs over and over again. We ran for weeks, repeating routes and running new routes, all while wearing one watch on each wrist and carrying one watch in each pocket. In this way, we were able to test the GPS accuracy of up to 4 watches simultaneously. We could also test the optical heart rate monitor of 2 watches at a time, wearing one on each wrist. We never placed more than one watch on each wrist and one watch in each pocket to keep the GPS antennas from interfering with each other.

We also tried to run over bridges and next to bodies of water as much as possible to see if the watches mapped us as swimming instead of running. Afterward, we compared the distances, elevations, and mapping data, all while considering the limitations and features of each watch (e.g., does it have a barometric altimeter, etc.).

We found that a snug fit is imperative to get an accurate heart rate reading. The watches that didn't fit our testers as well usually reported skewed heart rate results. We also used a chest strap heart rate monitor while using one or more of the watches as a stable comparison control. Chest heart rate monitors are considered more accurate and are not affected so easily by fit. We also used the watches to monitor our sleep so we could review our resting heart rates. Since we were lying still and not sweating, sleep testing offered a more controlled environment for heart rate measurement testing.

Here we take a look at the accuracy of the Garmin Forerunner 945 on...
Here we take a look at the accuracy of the Garmin Forerunner 945 on a 5-mile run in town. This is one of the best tested as you can see it follows the paths almost perfectly. Where it veered, we were on the grass. Right on.
Photo: Amber King


Design is mainly a function of size, fit, comfort, raw materials, and subjective appearance. Larger watches will not fit all wrists. Smaller ones may fit all wrists, but they make it difficult to read the screen. We measured and weighed each one and noted whether they are difficult to wear under typical running and athletic clothing and if size affected the fit, and thus, the accuracy of the optical heart rate monitor. We also noted information about the type of strap used, its ability to quick release, and any other notable issues with buttons accidentally getting pressed while exercising.

A comparison of the Garmin Forerunner 645 Music (top) and the larger...
A comparison of the Garmin Forerunner 645 Music (top) and the larger Suunto 9 Baro. Which design do you prefer?
Photo: Amber King