How accurate is your fitness tracker or smartwatch?
By Hannah Walsh
All fitness trackers and smartwatches will capture your steps or calories burned, but if you're using one to meet a daily step goal or lose weight then you'll want to ensure it's accurate. We pound the pavements and take a turn on the treadmill to challenge the accuracy of every wearable we test.
We've found fitness trackers and smartwatches that capture data with no error, but others that over or understate data, or that are unreliable and inconsistent day to day. These devices will leave you wondering how much activity you've actually done, and will make it impossible to track any improvements in fitness over time.
Below you can see the accuracy scores for every wearable we've tested basic on metrics such as steps, distance and heart rate, plus how they fare overall. Enter a model you're interested in into the search bar at the top of the table to filter the results.
We also reveal the lengths we go to challenge the fitness tracking of every smartwatch or activity band on test, as well as how your device calculates important metrics, such as distance travelled.
Only logged-in Which? members can view the exclusive ratings in the table below. If you're not yet a member, sign up for a Which? trial to get instant access. If you're already a member then search the table below by brand or name, or sort it by star rating or score by clicking on the table headings.
Fitness tracker and smartwatch metric ratings
Ratings for steps, distance and calories are based on accuracy and reproducibility data for walking, running, and an everyday routine scenario. Heart rate is based on low, mid and high-level activity accuracy and reproducibility. Overall star ratings include accuracy and reproducibility for distance, steps, heart-rate and GPS. Correct as of September 2019.
How we uncover the most accurate step trackers
Our test participants walk on a calibrated treadmill at 4.8km/h for 10 minutes and run at 9-10km/h for 10 minutes. This means we can compare the trackers’ abilities to log steps taken, as well as distance travelled. We also put test participants through a series of daily tasks, such as loading and unloading the dishwasher and carrying shopping.
One device miscalculated step count by 63%, meaning you'd only have taken 3,700 steps when it says you've taken 10,000 steps.
Consistency is just as important as accuracy. If a tracker is accurate on some days but not on others, you won’t know whether you’re improving. So we repeat our walking test to see if the trackers consistently overstate, understate or hit the accuracy mark.
Wearables with the most accurate heart-rate tracking
Tracking your heart rate is one of the best ways to monitor improvements in health and fitness levels, so accuracy and consistency is important. Our testers strap on a heart-rate monitor before hitting the treadmill walking and running, and then taking a well-deserved rest. We compare the readings with the data from the fitness watch or activity tracker, and calculate the percentage difference between them.
Two of the activity trackers on test score just one star for heart-rate tracking.
How does my smartwatch or fitness tracker calculate distance?
While many of us will be aiming to beat our daily step goal, it's also interesting to know just how far you've travelled. And for those training for a particularly long hike, or perhaps a marathon, distance is an important metric.
There are two main ways that a fitness watch or activity tracker will calculate the distance you've travelled.
There are two main ways that a fitness tracker or smartwatch will calculate the distance you've travelled.
- GPS Models that have built-in GPS can track your distance at all times, even without your smartphone by your side - great for those that like to run without their mobile. Some devices that don't have built-in GPS will use the sensor on your phone to track distance. If this isn't available, distance travelled will be based on steps.
- Steps Trackers that don't have built-in GPS or use the GPS on your smartphone will calculate the distance you've travelled by the number of steps you've taken. Usually this will be based on an estimated stride length multiplied by the number of footfalls, but some trackers allow you to add your measured stride length to improve accuracy of distance tracking.
We've found trackers with built-in GPS and those without that did a great job of tracking distance travelled. But, we've also uncovered models that understated distance travelled based on step data by 30% or more - meaning you could end up walking or running further than you need to.
Accurate step tracking isn't always a guarantee of spot on distance tracking either. Read our guide to the top fitness trackers for 2019 to find out which are best for monitoring steps, heart-rate, running and more.