The Epworth Sleepiness Scale (ESS) measures a person's general level of daytime sleepiness - their average propensity to doze off or fall asleep in eight common everyday situations, such as sitting and reading or watching television. Rather than asking how sleepy someone feels at a single moment, it asks about the usual chance of dozing in each situation in recent times, which makes it a measure of trait-like sleep propensity rather than momentary drowsiness.
It is important to distinguish sleepiness from fatigue. The ESS captures the likelihood of falling asleep, not tiredness, low energy, or poor-quality sleep at night. A patient with severe insomnia may score low on the ESS despite feeling exhausted, because difficulty sleeping at night does not necessarily translate into dozing during the day.
02 - Origin & purpose
Where it comes from.
The ESS was developed by Dr Murray Johns at the Epworth Hospital sleep centre in Melbourne, and published in Sleep in 1991. Johns wanted a simple, self-administered way to quantify daytime sleepiness in sleep-clinic patients - particularly those with obstructive sleep apnoea, narcolepsy and idiopathic hypersomnia - that did not require laboratory testing.
It quickly became the most widely used subjective measure of daytime sleepiness worldwide, appearing in clinical practice, research trials and regulatory submissions. It takes two to three minutes to complete and is available in many validated translations.
03 - Scoring & cutoffs
How scoring works.
Each of the eight situations is rated 0-3 for the chance of dozing, giving a total score of 0-24. Scores of 0-10 are considered within the normal range (0-5 lower normal, 6-10 higher normal). Scores above 10 suggest excessive daytime sleepiness and warrant clinical evaluation: 11-12 is usually interpreted as mild, 13-15 as moderate, and 16-24 as severe excessive daytime sleepiness.
A high score is not a diagnosis - it indicates that the cause of sleepiness (sleep apnoea, narcolepsy, insufficient sleep, medication effects, depression) should be investigated.
Score
Severity
Interpretation
0–5
Lower normal
Lower normal daytime sleepiness.
6–10
Higher normal
Higher normal daytime sleepiness.
11–12
Mild
Mild excessive daytime sleepiness.
13–15
Moderate
Moderate excessive daytime sleepiness.
16–24
Severe
Severe excessive daytime sleepiness.
04 - Validation evidence
How well it performs.
In Johns' 1992 reliability study, the ESS showed high internal consistency in sleep-clinic patients and stable scores in healthy adults retested five months apart, with a single-factor structure. As a screening test for obstructive sleep apnoea, however, its accuracy is only fair: at the conventional >10 cutoff, sensitivity for identifying patients with an apnoea-hypopnoea index of at least 5 was 66%, and reported specificity across studies is modest. In patients with OSA starting CPAP, the minimum clinically important difference has been estimated at 2-3 points.
α 0.88
Internal consistency
Cronbach's α 0.88 in sleep-clinic patients; 0.73 in healthy students - Johns 1992
r = 0.82
Test-retest reliability
Over 5 months in healthy adults - Johns 1992
66%
Screening for OSA
Sensitivity at the >10 cutoff (AHI ≥5) - Rosenthal & Dolan 2008
2-3 pts
Meaningful change
MCID estimated at 2-3 points in OSA - Patel et al. 2018
05 - How it compares
How it compares to the alternatives.
Instrument
Items
Time
When to reach for it
ESS
8
2-3 min
Quantifying habitual daytime sleepiness; licensed - cannot be hosted here.
Insomnia severity and treatment response - available in the Aisel scale library.
STOP-Bang
8
1-2 min
Eight yes/no items for structured OSA risk screening before sleep testing.
PSQI
19
5-10 min
Global sleep quality over the past month.
Karolinska Sleepiness Scale
1
Seconds
Momentary (state) sleepiness during tasks or shifts.
Multiple Sleep Latency Test
Lab
Half a day
Objective sleep propensity when subjective reports are unclear.
06 - When to use it
Right tool, wrong tool.
The ESS is at its most useful when the clinical question is how sleepy a patient habitually is, and whether that sleepiness is changing with treatment. It is a severity and monitoring measure, not a diagnostic or case-finding test.
Reach for it when
-Quantifying habitual daytime sleepiness in suspected or confirmed sleep disorders.
-Tracking response to CPAP or wake-promoting treatment in OSA and narcolepsy.
-Documenting sleepiness severity for fitness-to-drive or occupational assessments, alongside clinical judgement.
Reach for something else when
-Standalone screening to rule out OSA - sensitivity is too low, and a normal score does not exclude sleep apnoea.
-Diagnosing any specific sleep disorder on its own.
07 - Confidence & precision
Reading the score with care.
Short-interval repeatability in clinical populations is lower than the five-month figure from healthy adults suggests, and later work has questioned how stable individual scores are between visits. Changes smaller than 2-3 points should not be over-interpreted; the MCID in OSA has been estimated at 2-3 points. Interpret single scores alongside history, bed-partner report and, where indicated, objective testing.
08 - Limitations
What it cannot tell you.
It is a subjective self-report and correlates only weakly with objective measures such as the Multiple Sleep Latency Test. Its accuracy as an OSA screener is only fair, and some studies suggest a lower cutoff (8) in sleep-clinic populations. Some items assume situations not all patients encounter (for example driving), which can deflate scores. Scores can be minimised deliberately, a particular concern in driving and occupational contexts. Short-interval test-retest repeatability in clinical settings is limited.
09 - Licensing, explained
How licensing works.
The ESS is copyrighted by M.W. Johns (1990-1997). All permissions, licences and official translations are administered by Mapi Research Trust through the ePROVIDE platform, acting as Dr Johns' agent worldwide.
Individual clinicians in clinical practice, students and unfunded academic researchers can obtain a licence free of charge after registration; funded academic research, healthcare organisations, commercial users and digital-health or IT platforms pay a licence fee.
Because Aisel is a commercial platform, we cannot reproduce the questionnaire here. Clinicians who wish to use the ESS should register at eprovide.mapi-trust.org or epworthsleepinessscale.com.
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