The Least Accurate Fitness Trackers For Distance, According To Which?

One tracker underestimated the distance of a marathon by 10.8 miles.

If you plan to wear a fitness tracker while running the London Marathon this weekend, you might be surprised by how many miles it reports you’ve done.

Consumer watchdog Which? has exposed the least reliable fitness trackers on the market – with one underestimating the distance of a full marathon by nearly 11 miles.

The researchers tested trackers from big brands including Apple, Fitbit and Garmin. Bottom of the class was Garmin’s Vivosmart 4, which underestimated the distance covered by 41.5% – this means runners aiming for a 26.2-mile marathon could actually be running 37 miles if they relied on this tracker.

To put that into perspective, marathon runners on Sunday would cross the finish line at Buckingham Palace, carry on running south and continue all the way to South Croydon. Can you belie?

RobertoDavid via Getty Images

At the other end of the scale, a runner relying on the Huawei Watch 2 Sport tracker could find themselves around seven miles short of the marathon finish line – at the 19-mile mark – as the research indicated this model overestimates distance by 28%.

Which? tested 118 fitness trackers and smartwatches. The below table shows the least reliable trackers, based on distance while running, from each of the eight biggest brands:


Apple fared relatively well in the tests. Of the eight Apple models tested, the most inaccurate was the Apple Watch Series 3 GPS, which overestimated distance covered by 13% – around three miles under the finish line of a marathon. The best Apple model – the Apple Watch Series 1 – only overestimated distance while running by 1%.

The study uncovered other considerable variations within brands. For example, the Garmin Vivoactive 3 was 100% accurate at tracking running distance in tests, yet the Garmin Vivosmart 4 underestimated distance covered by 41.5%, and the Garmin Vivosmart HR overestimated by 30%.

Which? contacted Huawei and Garmin for responses to its investigation, as they were the two brands with the greatest inaccuracies – but they also informed the other brands of the findings.

A spokesperson from Garmin said the Vivosmart 4 does not incorporate GPS. “Our recommendation for someone who is running long distances such as a marathon, would be to choose a tracking device such as our Forerunner range which is dedicated to running and incorporates GPS,” they added.

A spokesperson for Huawei said the results may vary depending on testing conditions, such as indoor and outdoor environments and individual runner variances. “With regards to running indoors, as this particular test was carried out on a treadmill, the algorithm of the Huawei Watch 2 Sport tracks the distance by evaluating the data of user’s stride length and steps,” the spokesperson said.

“The results may deviate owing to individual runner variances. Huawei is fully committed to providing accurate and better running experience for users, and we will continuously work to optimise our existing and new generation products.”