In order to calculate sleep quality, Pillow takes into account body motions during sleep, as registered by the device’s accelerometer and gyroscope, as well as the noise level recorded by the microphone. These data are processed through a scientifically backed algorithm to calculate your sleep quality index.
As you continue using Pillow, sleep quality adapts to your personal sleep patterns, making the readings increasingly accurate. Overall quality typically ranges from about 25% for very poor, short, and disturbed sleep to around 90% for excellent sleep. Values outside this range usually reflect rare and extreme conditions (severe disturbances, chronic sleep disorders, or very poor sleep environments).
In terms of sleep stage durations, research indicates that normal ranges vary by age and sleep type:
Awake: 0–15% of the session (0–10% for naps)
Light sleep: 25–45% for young adults (18–50), 25–55% for older adults (50+); 25–55% for naps
Deep sleep: 18–30% for young adults, 15–30% for older adults, 12–30% for seniors; 10–40% for naps
REM sleep: 18–30% for young adults, 15–30% for older adults, 12–30% for seniors; 5–15% for naps
These values are averages, and they can vary depending on factors such as age, sex, weight, health condition, and sleep environment.
Pillow tracks sleep using two main setups:
Apple Watch: Combines motion detection and heart rate monitoring for a precise assessment of sleep stages and wakefulness.
iPhone only: Relies on motion data from the accelerometer and gyroscope, along with ambient sound recordings. While effective, this method is generally less accurate than tracking with Apple Watch.
Sleep quality scores are interpreted on a simple scale where scores above 80% typically indicate high-quality sleep. This helps you easily understand how restful your sleep was on a given night.