Metric
Sleep
What your sleep score is built from, why it moves, and what the stages and totals actually mean.
Sleep scores feel precise, but they're built from estimates, and they don't always match how rested you feel. A good night can score badly and a short night can score well. Here's what the research says these numbers are really tracking, what moves them, and how much weight to put on the score versus the trend.
What your device actually calls this
Scientific measurementSleep architecture (light/deep/REM stages) via actigraphy (movement) and/or heart rate-derived signals, not EEG, which is what defines "real" sleep staging in a lab.
| Device | What they call it | What it actually measures |
|---|---|---|
| Oura | "Sleep Score" | 7 inputs: total sleep time, efficiency, restfulness, REM duration, deep sleep duration, latency, timing consistency. |
| Whoop | "Sleep Performance" | 4 inputs: sleep sufficiency (hours vs. needed), sleep consistency (vs. prior 4 nights), sleep efficiency, sleep stress. |
| Garmin | "Sleep Score" | Incorporates a separate stress metric derived from HRV, alongside sleep stages. |
| Fitbit | "Sleep Score" | Combines heart rate, total time asleep, and sleep-stage breakdown into one 0-100 number, grouped into four bands from Poor to Excellent. Available on the free tier. |
| Apple Watch | "Sleep Stages" (no composite score) | Since watchOS 9, estimates Awake/REM/Core/Deep stages from motion, heart-rate dynamics, and circadian timing. Apple deliberately reports no single Sleep Score, the only brand here that doesn't score sleep at all. |
| RingConn | Sleep stages, breathing rate, skin temperature | A real published validation exists: a joint RingConn/Shanghai Ruijin Hospital dataset compared the ring against polysomnography, the clinical gold standard. |
| Samsung Galaxy Watch | "Sleep Score" and "Sleep Coaching" | Sleep Score runs 1-100 from four inputs; Sleep Coaching layers HRV, SpO2, and respiratory rate over 4-5 weeks into a personalized plan. |
| Ultrahuman Ring | "Sleep Algorithm 2.0" | Machine-learning model trained on 125,000+ nights. Ultrahuman's own 6-participant pilot study reported 2.4-2.6% mean absolute error against an FDA-approved reference device, but it's self-published, not independently peer-reviewed. |
| Coros | "Sleep Score" and "Sleep Stress" | Stages graded against National Sleep Foundation thresholds; Sleep Stress separately flags physical/mental strain from elevated heart rate and lowered overnight HRV. |
| Amazfit | No standalone Sleep Score | Sleep tracking feeds directly into the next morning's Readiness Score rather than standing alone as its own branded score. |
| Polar Vantage | "Sleep Plus" | Tracks stages, continuity, and quality, feeding results into Recovery Pro alongside HRV and training data. |
Oura, Whoop, Garmin, and Fitbit all call it a "Sleep Score" or close to it, but the actual formulas weigh meaningfully different things, and Apple breaks from all four by reporting no composite score at all. Oura leans on stage architecture, Whoop on performance/consistency framing, Garmin folds in a stress signal the others don't, and Fitbit's formula is the simplest of the four scored brands. A Sleep Score from one device isn't measuring the same combination of things as another's, even at the same numeric value.
Device measurement accuracy: Emerging · see the fileHow each device actually shows this
Oura
"Sleep Score"
Whoop
"Sleep Performance"
Garmin
"Sleep Score"
Fitbit
"Sleep Score"
Apple Watch
"Sleep Stages" (no composite score)
RingConn
Sleep stages, breathing rate, skin temperature
Samsung Galaxy Watch
"Sleep Score" and "Sleep Coaching"
Ultrahuman Ring
"Sleep Algorithm 2.0"
Coros
"Sleep Score" and "Sleep Stress"
Amazfit
No standalone Sleep Score
Polar Vantage
"Sleep Plus"
See every device →
Sources: Oura's own support docs (support.ouraring.com) and Whoop's own published sleep-accuracy page (whoop.com), both primary. Fitbit/Google's own support documentation (official). Apple's own support documentation (official). Garmin's stress-in-sleep-score detail came from a secondary comparison source.
The benchmark
Sleep
Sleep Score Explained: What Is a Good Sleep Score?
What goes into the number and what it can and can't tell you.
See how you compareExample result
Age 40 ยท 6.5 h
just below the recommended range
NSF expert consensus
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