Oura vs WHOOP — which gives more accurate HRV readings?

Oura Ring and WHOOP both measure HRV via photoplethysmography (PPG) during sleep; independent validation studies show Oura has somewhat stronger agreement with polysomnographic ECG-derived RMSSD (mean absolute error approximately 7–9 ms) compared to earlier WHOOP generations (mean absolute error 10–14 ms), though WHOOP's algorithm has improved in recent generations and the difference in clinical meaningfulness is modest (de Zambotti et al., npj Digital Medicine, 2019).

The more important truth is that neither device should be compared against the other's absolute numbers, they are measuring the same underlying physiology with different sensor placements and algorithms, so a "45 ms" from Oura and a "45 ms" from WHOOP are not equivalent values. Use each device's readings relative to your own personal baseline on that device. The within-person trend reliability (is my HRV going up or down over time?) is high for both devices. The between-person comparison (my friend's WHOOP says 60 ms and mine says 40 ms) is not valid without knowing device type, algorithm version, and individual baseline differences.

Honesty Scale: Promising (2) for both devices as HRV trend trackers. Insufficient clinical validation to call either a diagnostic medical device.

What to do: Pick one device and stick with it for trend analysis. Do not switch devices mid-protocol and compare the numbers, your baseline will shift. The consistency of measurement on one device over 90 days is worth more than switching to a "more accurate" device and restarting your baseline.

For the full picture, read Your Whoop Is Worried. Here Is What It Actually Found.