How to Choose a Sports Watch: What Studies Actually Measure
Product pages list dozens of features, and it's hard to know which ones matter. Here's what studies have measured on sports watches, and how to work out what you need.
The KILYO team
The sports coach that reads your workouts
The short answer
Pick the watch whose GPS, battery life and comfort fit your sport and your longest workout. A 2020 study of eight GPS watches, published in JMIR mHealth and uHealth, found an average distance error of 3.2% to 6.1% in town, in forest and on open ground. Wrist heart rate is more variable, and no brand is accurate for calories.
Key takeaways
- GPS distance error is low to moderate: 0.6% to 1.9% on a 56 km ultra, 3.2% to 6.1% on mixed routes, with possible underestimation of up to 9%.
- Wrist heart rate is more variable than step counting, and no brand is accurate for calories.
- Don't treat calories as an exact measure, and read VO2max over several weeks rather than a single day.
- The right choice starts with your sport, your longest workout, and how you plan to use the data.
A sports watch shows dozens of data points: pace, heart rate, calories, VO2max, training load. They don't all carry the same weight. GPS distance is the most reliable. Most of the rest are estimates, best read as trends.
The good news: you don't need to compare twenty models. Once you know what studies have measured, you know what to expect from your watch and what to ignore on the product page.
Start with how you train, not with features
Before you look at any model, answer three questions. What sport do you do? What's your longest workout? What do you want from the data: track your volume, guide your workouts by pace or heart rate, or prepare for a race?
Volume is the simplest to track, and the WHO gives the benchmark for adults:
If you're just starting out, those minutes matter more than how sophisticated the device is. A watch that records time, distance and heart rate well is enough. To structure your weeks, you can lean on improving your running with 3 sessions a week.
GPS: a low to moderate error
Two studies measured distance accuracy. A team from the Swiss Federal Institute of Sport in Macolin tested eight GPS watches while walking, running and cycling, in town, in forest and on open ground. The average absolute error ranged from 3.2% to 6.1% depending on the watch, and distance can be underestimated by up to 9%.
On 10 km, a 3% error means roughly 300 m of difference. That's fine for following a workout, but keep it in mind if you want to compare two runs to the meter.
On a 56 km ultramarathon, other researchers found better results: 0.6% to 1.9% error compared with timing mats. The gap makes sense. The ultra was run on an open course, while the Macolin study also tested town and forest, where the signal is less clean. The authors also recommend these watches mainly for open terrain. In forest or town, expect the higher end of the error range.
These studies cover models from 2020 or earlier. They tell you what to expect from GPS in general, not how a specific recent model performs.
Wrist heart rate: compare it once with a chest strap
Try this: on one workout, wear a chest strap and your watch, then compare the two heart rate traces. You'll see how well your wrist tracks your effort.
Why? A 2020 systematic review of consumer watches and bands found that heart rate is measured more variably than steps. Apple Watch and Garmin were the most accurate, while Fitbit tended to underestimate. That review covers consumer devices in general, not running watches specifically.
So the wrist gives a useful but variable reading. Check your pace and how you feel too, rather than relying on one number.
If you want to set your workouts by heart rate, start by calculating your zones:
Free calculatorHeart rate zonesOpen the calculator →Calories and VO2max: how to use them
For energy expenditure, the same review is clear: no brand was accurate. Ignore the calorie count when working out what to eat: treat it as a very rough ballpark.
The VO2max shown on your watch is also an estimate and doesn't replace a lab test. Studies give mixed results: sometimes valid, sometimes overestimated, sometimes underestimated. To be safe, watch the trend over several weeks rather than a single number. To compare it with another method, try the VO2max calculator and the VMA calculator.
Practical criteria that matter day to day
A watch you don't wear, or one that dies before the end of your run, measures nothing.
- Battery life: make sure it lasts well beyond your longest workout with GPS on. For a long trail run or an ultra, this is a major factor.
- Comfort: weight, strap, case size. You'll wear it for hours, sometimes overnight.
- Display: readable in bright sunlight, with physical buttons if you sweat a lot or wear gloves.
- Compatibility: can you export your workouts to Strava or your coaching app?
- Multisport mode: essential for triathlon, so you can move from swimming to cycling to running without stopping everything. If you're getting into it, see getting started in triathlon with three sessions a week.
What you can do at your next workout
A watch is only worth what you do with it. Here's a checklist to help you choose, or to check the one you already have:
- I've noted my main sport and my longest workout.
- The stated battery life is longer than that workout, with GPS on.
- I've tested the distance on a route I know.
- I don't use calories as an exact measure, and I track VO2max over several weeks.
- My workouts export to the app I use for my plan.
Then check the same three numbers at every workout: pace, heart rate and duration. If your watch syncs with Strava or Garmin, KILYO reads your workouts (Garmin, Apple Watch, Coros, Polar, Suunto, Strava and more), analyzes pace, heart rate, volume and consistency, then adjusts your plan.
Frequently asked questions
Which sports watch should I get to start running?
A simple watch with GPS and wrist heart rate is enough. Focus on comfort and battery life. GPS distance has a low to moderate error, accurate enough to track your workouts.
Do I need a chest strap, or is the wrist sensor enough?
The wrist gives a useful but variable reading: the 2020 review found it less consistent than step counting. If you train by heart rate, compare one workout with a chest strap before trusting the wrist reading.
Are the calories my watch shows reliable?
No. In the 2020 review, no brand was accurate for energy expenditure. Don't use them to plan your food.
Does a high-end watch really improve progress?
A watch measures, it doesn't make you improve. Your training does that. Choose it for how you train and for your consistency.
Sources
- Fuller D., Colwell E., Low J., et al. (2020). Reliability and Validity of Commercially Available Wearable Devices for Measuring Steps, Energy Expenditure, and Heart Rate: Systematic Review. JMIR mHealth and uHealth. DOI
- Gilgen-Ammann R., Schweizer T., Wyss T. (2020). Accuracy of Distance Recordings in Eight Positioning-Enabled Sport Watches: Instrument Validation Study. JMIR mHealth and uHealth. DOI
- Johansson R. E., Adolph S. T., Swart J., Lambert M. I. (2020). Accuracy of GPS sport watches in measuring distance in an ultramarathon running race. International Journal of Sports Science & Coaching. DOI
- Bull F. C., Al-Ansari S. S., Biddle S., et al. (2020). World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine. DOI
Written with the help of AI.
