What Is the Karolinska Sleepiness Scale?

The Karolinska Sleepiness Scale (KSS) is a one-question rating of how sleepy you feel right now, from 1 (extremely alert) to 9 (very sleepy, fighting sleep). It takes seconds, and it’s been validated against brain activity and performance: scores above 6 are linked to slower reactions, lapses of attention, and impaired driving.

This article is general information, not medical advice. If you’re often very sleepy during the day despite enough sleep, talk to a doctor.

The Scale

Choose the description that matches how you’ve felt over the past 10 minutes:

Score	Description
1	Extremely alert
2	Very alert
3	Alert
4	Rather alert
5	Neither alert nor sleepy
6	Some signs of sleepiness
7	Sleepy, but no effort to keep awake
8	Sleepy, some effort to keep awake
9	Very sleepy, great effort to keep awake, fighting sleep

Åkerstedt and Gillberg introduced the scale in 1990 at the Karolinska Institute in Stockholm. It measures your state at one moment, unlike questionnaires such as the Epworth Sleepiness Scale, which ask how likely you usually are to doze off in daily situations.

What the Scores Mean

• Validation. Kaida and colleagues found that as KSS scores rose, so did reaction times, lapses of attention, and the brain-wave signs of sleepiness, showing that the ratings track real changes in alertness.
• Above 6. In a 2014 review, Åkerstedt and colleagues concluded that KSS rises sensitively with lost sleep and night work, and that scores above 6 are associated particularly with impaired driving and with brief intrusions of sleep into the waking brain.

So a 7 or more while driving is a reason to stop and rest, not push on.

How to Use It

Because it’s quick, KSS is good for repeated ratings:

• At set times, such as mid-morning and mid-afternoon, to see your daily pattern, including the familiar dip after lunch.
• After changes, such as a short night, a late coffee, or a new bedtime, to see what they do to your alertness.
• Before driving, as a check on yourself.

Rate honestly and quickly, without thinking about what the score “should” be.

Following It in Kaizora

Karolinska Sleepiness Scale Score is on the Sleep page; log a rating with Log whenever you want, at the time you felt it. On Correlations, put your daily average beside Total Sleep Time or Dietary Caffeine to see what moves it. A habit such as “at least once a day” on it keeps the ratings regular; see Habits.

The Short Version

• KSS rates how sleepy you feel right now, from 1 to 9.
• Scores above 6 are linked to impaired attention and driving.
• Rate at set times and after changes to see what drives your sleepiness.

Sources

• Åkerstedt T, Gillberg M, “Subjective and objective sleepiness in the active individual,” International Journal of Neuroscience 52, no. 1–2 (1990): 29–37. doi:10.3109/00207459008994241
• Kaida K et al., “Validation of the Karolinska sleepiness scale against performance and EEG variables,” Clinical Neurophysiology 117, no. 7 (2006): 1574–1581. doi:10.1016/j.clinph.2006.03.011
• Åkerstedt T et al., “Subjective sleepiness is a sensitive indicator of insufficient sleep and impaired waking function,” Journal of Sleep Research 23, no. 3 (2014): 242–254. doi:10.1111/jsr.12158