Karolinska Sleepiness Scale (KSS) — Single-Item Sleepiness Test

The Karolinska Sleepiness Scale (KSS) is a single-item, 9-point Likert scale used to measure momentary sleepiness. It was developed for research and clinical settings to provide a rapid subjective assessment of how sleepy a person feels at a specific time.

Use the KSS whenever you need to assess current alertness — for example, before driving, during work shifts, or at set intervals for research. Many users take it hourly during wake periods or at key points (morning, mid-afternoon, evening) to track trends. Choose a consistent schedule that matches your goals.

Scores 1–3 indicate alertness, 4–6 indicate mild to moderate sleepiness, and 7–9 indicate high sleepiness with potential performance impairment. High scores (7 or above) suggest you should avoid risky activities and seek restorative sleep or medical advice if persistent.

KSS is widely used in research and occupational safety to monitor acute sleepiness and fatigue. While useful as a quick screening tool, it should complement objective measures (e.g., performance tests, actigraphy) and clinical evaluation when diagnosing sleep disorders or making safety-critical decisions.

As a single-item subjective measure, the KSS captures perceived sleepiness at a moment in time but does not provide information about chronic sleep quality, sleep architecture, or objective performance deficits. Self-report can be influenced by bias, so combine KSS data with behavioral or physiological measures when possible.

If you regularly score 7 or above, prioritize sleep hygiene (consistent schedule, dark/quiet sleep environment, reduce stimulants), consider strategic naps and schedule changes, and consult a healthcare professional to evaluate for sleep disorders, medication effects, or other medical conditions contributing to excessive daytime sleepiness.