How accurate is the Apple Watch's step counter and distance tracking?

CNET's Dan Graziano tested the step and distance accuracy of the Apple Watch. See how it stacks up against the competition.

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Sarah Tew/CNET

There's no doubt that the Apple Watch can do a lot of things. It can be used to communicate with others, view notifications from an iPhone and even pay for items with Apple Pay. It's also a dedicated activity tracker that can measure active calories burned, active minutes, the number of times you stand throughout the day, your daily step count and distance traveled.

We've been testing the Apple Watch over the past few weeks, and focused on those final two metrics -- steps taken and distance traveled -- to see how it stacks up against the competition.

How the Apple Watch measures distance

To be clear, steps taken and distance traveled are two related -- but discrete -- metrics. The former is exactly what it sounds like: the number of footfalls in a given period, while the latter is the resulting linear distance. While both should be absolute numbers, they'll differ from person to person based on height and stride.

But take nothing for granted. Yes, a taller person should be able to cover a fixed distance with fewer steps. But depending on his or her pace (say, an active run versus a casual walk), the number of steps in a given mile or kilometer can also vary for an individual.

So, how does the Apple Watch convert steps to distance? During your first day with the device, you will be asked to provide the Watch's activity app with basic health information, such as height, gender, age and weight. Apple will then use this information to estimate your calorie burn and stride length, which in turn is used for the distance metric. Companies like Fitbit and Jawbone also attempt to estimate calorie burn and distance using health information you provide during set up.

Activity trackers from Fitbit and Garmin allow you to set a custom stride length to calibrate the device for improved accuracy. The Apple Watch also offers an option to calibrate, but the process is less tedious. Steps and distance on the Apple Watch can be calibrated using your iPhone's GPS. This will establish an individual benchmark for how many of your steps are in an average mile. Once established, the Watch can then make an educated guess on distance traveled, whether or not your iPhone is present and connected. You can learn how to calibrate the Apple Watch here.

The test

With those caveats in mind, I developed a testing methodology to try and reduce variables as much as possible. I wore each activity tracker or smartwatch on my left wrist at a single time and walked on a treadmill for a mile (as measured by the treadmill's built-in distance tracker). I then compared the mileage from the treadmill to the mileage recorded on the watch. This test was performed three times with each device I tested to ensure accuracy. The same treadmill was used for the test, and I walked at the same speed (3.5 mph, which came to about 17 minutes each time).

The charts below show the results, with steps and distance traveled being the average of the three walks for each device. Each tracker was tested in an original out-of box state, unless otherwise noted.

Activity trackers

Device Steps Distance (mi) Difference* Deviation*
Apple Watch (calibrated) 2,097 avg 1.003 avg 0.003 0.3%
Garmin Vivosmart 2,079 avg 1.01 avg 0.01 1%
Lifetrak Zone C410 2,120 avg 0.96 avg -0.04 4%
iFit Active 2,166 avg 0.96 avg -0.04 4%
Misfit Shine 2,102 avg 0.93 avg -0.07 7%
Fitbit Charge 2,108 avg 0.91 avg -0.09 9%
Apple Watch (out of the box) 2,107 avg 1.10 avg 0.1 10%
Pivotal Tracker 1 2,083 avg 0.84 avg -0.16 16%

Smartwatches

Device Steps Distance (mi) Difference* Deviation*
Apple Watch (calibrated) 2,097 avg 1.003 avg 0.003 0.3%
Samsung Gear S 2,082 avg 1.02 avg 0.02 2%
Garmin Vivoactive 2,086 avg 1.02 avg 0.02 2%
Microsoft Band 2,111 avg 0.97 avg -0.03 3%
Fitbit Surge 2,107 avg 0.93 avg -0.07 7%
Samsung Gear 2 Neo 2,103 avg 1.08 avg 0.08 8%
Moto 360 2,190 avg 0.91 avg -0.09 9%
Apple Watch (out of the box) 2,107 avg 1.10 avg 0.1 10%
Samsung Gear Fit 2,116 avg 1.10 avg 0.1 10%

*As measured on device vs. 1 mile as measured on a gym treadmill

Step counts for the 14 activity trackers and smartwatches we tested ranged from 2,079 to 2,190. The 2,097 and 2,107 average steps measured by the uncalibrated and calibrated Apple Watch placed it in the middle of the pack. (The treadmill does not measure steps, so we can only compare step counts among tested devices.)

In its out-of-the-box, precalibrated state, the Apple Watch lagged on distance measurement: both it and the Samsung Gear Fit consistently overestimated the distance I walked compared to the data recorded by the treadmill. The distance tracked on both devices were off on average by 10 percent, with only the $12 Pivotal Tracker 1 performing worse with a 16 percent deviation. Once calibrated, however, the Apple Watch jumped to the head of the pack, with a deviation of just 0.33 percent.

The Moto 360 , on the other hand, was found to be the most inconsistent device in our test. The step results from all three of the test we performed with the watch were higher than the other 13 devices tested. In our first test, our steps were recorded at 2,207, the second test was the highest at 2,248, and the last was 2,115, for an average of 2,190 steps walked.

The mileage metric on the Moto 360 saw even greater inconsistencies, measuring 0.92 in our first test, 1.08 in the second, and dropping to 0.74 in the third, compared to the mileage recorded on the treadmill. These inconsistencies aren't just isolated to the Moto 360, however, but appear to be a problem in the way Google Fit measures steps and the algorithm used to convert them to distance. We reached out to Google about this issue, however a Google spokesperson declined to comment.

Devices not included in the test

We attempted to test a diverse range of products from a variety of companies. That included brand name smartwatch and activity trackers, along with some lesser known models. Unfortunately, there are a handful of devices that weren't able make it into our test. The most prominent are activity trackers from Jawbone, including the Up Move, Up24, Up2 and Up3, and Android Wear watches. These were left out because of the way they sync with the Jawbone app; the information isn't visible in real-time, which made it difficult to measure the true distance we walked.

What does it mean?

While we endeavored to make this test as scientific as possible, make no mistake: you should take the results with a grain of salt.

For starters, the data presented here presumes that our test treadmill was accurately and consistently measuring one mile during each of our walks, over a testing period that lasted several months. (We've been amassing the data on these products for a while.)

And -- even if our testing was 100 percent accurate -- your real-world experience with these activity trackers will almost certainly not be. For instance, these devices can confuse activities like washing the dishes or lifting weights as "steps," because they're generally measuring the swing of your arm more than anything you're doing with your feet.

And, as always, these devices are subject to an endless array of software and firmware updates, in which the manufacturers are constantly tweaking and modifying measurements and data collection across the board. Each company uses its own algorithm to measure distance and no two trackers will give the same result.

But perhaps the biggest takeaway is that the accuracy of the device is less important than its consistency. If you stick with any one device, and it's 5 percent off every day, you'll at least have a record of your daily progress relative to your previous performance. (Your bathroom scale may not be providing your "actual" weight either, but if it's consistent, it should be letting you know if you're gaining or losing weight with each weigh-in.) The idea behind using these devices is simply to motivate you to walk more each day.

The most accurate distance trackers are ...

While some devices don't even include a calibration option, most people don't bother to calibrate those activity trackers and smartwatches that do include the feature. Unfortunately, the calibration method of measuring stride length isn't all that simple to perform. Apple's calibration technique, on the other hand, requires a 20-minute outdoor walk with your iPhone. I highly recommend you calibrate the Apple Watch if you care about accuracy.

While the Apple Watch takes the accuracy crown once it's calibrated, it's also worth saluting the three devices that delivered the most reliable out-of-box results in our test. If you want to be certain of your exact distance and aren't interested in calibrating your device, the Garmin Vivosmart , the Samsung Gear S and the Garmin Vivoactive are your best choices -- for now.

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