Wearable Accuracy: What Oura, Whoop and Apple Watch Actually Measure Well

Consumer wearables like Oura, Whoop, and Apple Watch use a combination of optical heart rate sensors, accelerometers, and skin temperature sensors to estimate everything from sleep stages to heart rate variability to calories burned. Validation studies comparing these devices against gold-standard laboratory measurements, like polysomnography for sleep or metabolic carts for energy expenditure, have found accuracy varies considerably depending on which specific metric is being measured.

Heart rate and heart rate variability tend to be measured reasonably accurately by most modern wearables, particularly at rest. Sleep stage classification, distinguishing REM from deep from light sleep, tends to be considerably less accurate compared to clinical polysomnography, even though basic sleep versus wake detection is fairly reliable. Calorie burn estimates, particularly during exercise, are generally considered the least accurate metric across most consumer devices, often varying substantially from indirect calorimetry measurements.

Why this matters for tracking: knowing which specific metrics a given wearable measures well, versus which ones are closer to rough estimates, changes how much weight you should put on any single number the device reports.