WRISTGRID BLOG
How a sleep score is calculated
You wake up, glance at your watch, and see a single number: your sleep score. But what makes a night a 92 instead of a 68? It's not just how long you slept. Here's how a sleep score is actually built — and the surprising reason that sleeping too long can lower it.
It's not just duration
Most people assume a sleep score is mostly about hours in bed. Duration matters, but it's only part of the picture. A well-built sleep score weighs three things: how long you slept, the structure of that sleep (your stages), and how efficiently you slept.
In WristGrid, duration carries the most weight, but sleep stages and efficiency each account for a meaningful share. That's why two nights of "eight hours" can score very differently — one might be deep and unbroken, the other shallow and restless.
Duration: the 7–9 hour sweet spot
Sleep-duration scoring follows the research consensus (the American Academy of Sleep Medicine recommends 7–9 hours for adults). A night in that window scores highest. Shorter nights score progressively lower, with the steepest drop below five hours.
Here's the counterintuitive part: sleeping much longer than nine hours also scores slightly lower. Chronic oversleeping is often a signal of poor sleep quality or an underlying issue, so the model gently penalizes it rather than rewarding it. More is not always better.
Stages and efficiency: the hidden 60%
Sleep structure looks at whether you got enough of the restorative stages. Deep sleep (physical recovery) and REM sleep (mental and emotional processing) each have healthy ranges as a share of your total night. Too little deep or REM sleep pulls your score down — even if your total hours looked fine.
Efficiency measures how much of your time in bed was actually spent asleep. If you were in bed for nine hours but asleep for six and a half, your efficiency is low, and that restlessness costs you. This is why the score rewards a consolidated, uninterrupted night over a long but broken one.
Using your sleep score to sleep better
The most useful way to read a sleep score is as feedback on your habits, not a verdict. A run of low scores after late nights, alcohol, or evening stress is your body showing you the cost. A high score after a consistent bedtime is confirmation it's working.
WristGrid puts your sleep score on your iPhone, so it's the first thing you see in the morning — along with the duration, stages, and resting heart rate behind it, synced automatically from your watch overnight.
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