Accurate enough for casual use, but serious runners will want more
In the quiet arithmetic of a 10-kilometer run on a sweltering UK evening, two devices — one costing $99.99, the other $799 — were asked the oldest question in sport: how hard did you work, and how far did you go? The answers were, in part, the same. Where they diverged reveals something enduring about the relationship between price, purpose, and the tools we choose to know ourselves.
- A screenless $99.99 Fitbit Air and an $799 Apple Watch Ultra 3 were strapped to opposite wrists for a live 10km comparison — the gap in price demanding a reckoning with the gap in performance.
- Heart rate and calorie readings landed within striking distance of each other — just 3bpm and fewer than 25 calories apart — suggesting the budget device punches well above its weight on the metrics most people actually care about.
- The fault line opened at GPS: the Fitbit Air, borrowing location data from a paired iPhone rather than carrying its own chip, overestimated pace by 10 seconds per kilometer and inflated distance by more than 400 meters.
- The Apple Watch surfaced richer biomechanical detail — stride length, vertical oscillation — while the Fitbit offered step count instead, each device quietly optimised for a different kind of runner.
- The comparison lands on a clean fork in the road: casual fitness users get reliable core data at a fraction of the cost, while serious runners chasing precision will need onboard GPS and dedicated hardware.
On a sweltering UK evening, a tester set out on a 10-kilometer run with a Google Fitbit Air on one wrist and an Apple Watch Ultra 3 on the other — an eight-to-one price difference compressed into a single workout. The question was simple: does the cheaper device actually deliver?
Both trackers use optical heart rate sensors and derive calorie estimates from movement and pulse data. The key structural difference is GPS — the Apple Watch carries it onboard, while the Fitbit Air borrows location data from a paired iPhone. A Polar H10 chest strap was meant to serve as a reference, but malfunctioned mid-run, leaving the two wrist devices to speak for themselves.
On heart rate and calories, the results were remarkably close. Average heart rate differed by just 3 beats per minute, and calorie counts diverged by fewer than 25 — a performance that placed the Fitbit Air in credible company with a device Apple has previously matched against dedicated electrical monitors.
The GPS data told a different story. The Fitbit overestimated pace by 10 seconds per kilometer and recorded the distance as 10.43km against an actual route of 10.03km — more than 400 meters of phantom ground. Both devices drew identical maps to the same finish line, yet their derived metrics diverged meaningfully. The tester, aware the run had felt slower than usual due to heat and elevation, found Apple's assessment more believable.
The Apple Watch also offered stride length and vertical oscillation data; the Fitbit returned a step count of 9,342 that the Apple Watch never surfaced. Neither was wrong — they were simply built for different conversations.
The conclusion is less a verdict than a sorting mechanism. For anyone tracking cardiovascular effort and energy expenditure, the Fitbit Air earns its place at $99.99. For runners who need precise pace, accurate distance, and biomechanical feedback, the absence of onboard GPS is a real constraint — and the search for the right tool will lead elsewhere.
On a sweltering evening in the UK, a tester strapped two fitness trackers to opposite wrists and set out on a 10-kilometer run. One was the newly released Google Fitbit Air, a screenless device priced at $99.99. The other was the Apple Watch Ultra 3, a premium smartwatch that costs $799. The question was straightforward: how do they actually perform when you're trying to track a workout?
The Fitbit Air arrived with considerable fanfare—Google's entry into the fitness tracker market with an AI-powered health coach and a price point that undercuts Apple by a factor of eight. But early adopters had already voiced frustration over app changes and missing features. This test was designed to answer a more fundamental question: does the cheaper device deliver accurate data where it matters most?
Both devices rely on optical heart rate sensors—LED lights that measure blood flow through the wrist to estimate your pulse. Both calculate calories burned by combining heart rate data with movement metrics. The key difference is GPS. The Apple Watch has it built in. The Fitbit Air does not, instead borrowing location data from the paired iPhone. The tester also wore a Polar H10 chest strap as a reference point, though it malfunctioned during the run, eliminating that benchmark.
The results were striking in their similarity. The average heart rate readings differed by just 3 beats per minute—Apple Watch at one figure, Fitbit Air at another. The calorie counts were even closer, with the Fitbit exceeding the Apple's calculation by fewer than 25 calories. On paper, this suggested the Fitbit's optical sensor was performing at a level comparable to Apple's, which in previous tests had matched dedicated electrical heart rate monitors exactly. For someone buying a fitness tracker to monitor their cardiovascular effort and energy expenditure, this was reassuring news.
But the GPS story told a different tale. The Fitbit Air overestimated the pace by 10 seconds per kilometer, suggesting the run was faster than it actually was. It also inflated the total distance to 10.43 kilometers when the actual route was 10.03 kilometers—a difference of over 400 meters. Both devices displayed identical maps with the same finishing point, yet the Fitbit's GPS-derived metrics diverged significantly from the Apple Watch's. The tester, who knew the run felt slower than usual due to heat and elevation changes, found Apple's pace assessment more credible.
The Apple Watch also provided richer detail about the run itself: stride length, vertical oscillation (a measure of bounce), and other biomechanical data. The Fitbit offered something different—a step count of 9,342 during the workout, which the Apple Watch did not surface. Neither device was wrong, exactly. They were simply measuring different things.
The analysis hinged on a crucial distinction. For the metrics that depend on the wrist-based heart rate sensor—the core function of any fitness tracker—the Fitbit Air proved itself reliable and accurate, despite costing one-eighth as much as the Apple Watch Ultra 3. For casual users who want to know their heart rate and calories burned during a workout, the Fitbit delivers. But for anyone who cares about precise pace, distance, and running mechanics, the lack of onboard GPS becomes a real limitation. The Fitbit's reliance on the iPhone's GPS for location data introduced measurable error that a dedicated running watch would not tolerate. Serious runners, the kind who study stride length and vertical oscillation, would likely gravitate toward devices built specifically for that purpose. For everyone else, the Fitbit Air's accuracy at a fraction of the price might be enough.
Citações Notáveis
The Google Fitbit Air is very accurate compared to the Apple Watch Ultra 3 for metrics relying on the onboard heart rate monitor, but lacks the GPS precision that serious runners require.— Test findings
A Conversa do Hearth Outra perspectiva sobre a história
Why does the GPS matter so much if the heart rate and calories are nearly identical?
Because pace and distance are what runners actually use to measure improvement. A 10-second error per kilometer compounds over time. If you're training for a race, you need to know if you're actually hitting your target speed.
But the Fitbit is using the iPhone's GPS. Couldn't that be a one-time glitch?
Possibly. But the pattern was consistent—it overestimated pace and distance in the same direction. That suggests a systematic issue with how the Fitbit processes GPS data from the phone, not a random error.
So the Fitbit is basically accurate for casual users but not for serious runners?
That's the divide. If you're checking your heart rate and calories to stay generally fit, the Fitbit is plenty good and costs a fraction of the Apple Watch. But if you're training seriously, you need the precision that comes with dedicated hardware.
Why would Google design a fitness tracker without GPS?
Cost, probably. GPS chips add expense and complexity. For a $99 device targeting casual users, the assumption is that most people have their phone with them anyway. It's a trade-off.
Did the tester seem disappointed?
Not really. More measured. They acknowledged the Fitbit's strength—accurate heart rate and calorie data—while being honest about its limitation. The real question is whether you're the kind of person who needs what the Fitbit can't do.