Is the Samn-Perelli scale the same as the Karolinska Sleepiness Scale?

No. Samn-Perelli asks how tired you feel, on 7 points, while the Karolinska Sleepiness Scale asks how sleepy you feel, on 9 points. The 2025 airline study above used both.

Is a higher score better or worse?

Worse. 1 is fully alert and 7 is completely exhausted, so the number rises with fatigue.

Where does the name come from?

It is named for the two authors of the 1982 report, written at the US Air Force School of Aerospace Medicine at Brooks Air Force Base, Texas.

Samn-Perelli fatigue scale

Updated October 8, 2026 · 2 min read

The Samn-Perelli scale is a 7-point fatigue checklist: you pick the one statement that best matches how you feel right now, from 1, "fully alert, wide awake", to 7, "completely exhausted, unable to function effectively". It comes from a 1982 US Air Force School of Aerospace Medicine report on aircrew fatigue.

The seven levels, with a night-shift example

1Fully alert, wide awake
2Very lively, responsive, but not at peak
3Okay, somewhat fresh
4A little tired, less than fresh
5Moderately tired, let down
6Extremely tired, very difficult to concentrate
7Completely exhausted, unable to function effectively

The seven Samn-Perelli levels in the short wording used on this site, from 1 (fully alert, wide awake) to 7 (completely exhausted, unable to function effectively).

A higher number means more fatigue. Each rating describes the moment you make it, so the same person can score very differently a few hours apart.

Say you work an ED night from 23:00 to 07:00 after getting up at 07:00. At 23:00 you pick 2: very lively, but not at peak. At 03:00 you pick 4: a little tired. At 06:30, with handoff still ahead, you pick 6: extremely tired, with real trouble concentrating. Three quick ratings show the climb through the night.

In Capillary's My hours and Analytics, you can log one 1 to 7 rating after each shift, next to your hours, nights and quick returns.

The original 1982 wording

The scale is the fatigue half of the Crew Status Check (SAM Form 202), printed in the report's appendix. The form itself is dated July 1980. Crew members circled the one statement that described how they felt "right now".

Fatigue statements on the Crew Status Check, as printed in the 1982 report
Level	Wording on the form
1	"Fully Alert; Wide Awake; Extremely Peppy"
2	"Very Lively; Responsive, But Not At Peak"
3	"Okay; Somewhat Fresh"
4	"A Little Tired; Less Than Fresh"
5	"Moderately Tired; Let Down"
6	"Extremely Tired; Very Difficult to Concentrate"
7	"Completely Exhausted; Unable to Function Effectively; Ready to Drop"

The short wording on this site drops "extremely peppy" from level 1 and "ready to drop" from level 7. The levels are otherwise the same.

The same card carried a 7-point workload scale. According to the report, crews preferred the card to an older 10-item fatigue checklist and found it easier to use, and the two gave very highly correlated results. Aviation research still uses the scale: a 2025 study of Brazilian airline crews paired it with the Karolinska Sleepiness Scale.

What the scores meant to its authors

The report did not test cutoffs. Drawing on field experience with flight crews, its authors hypothesized what each score meant for performance:

1 to 3: alert enough, with no performance impairment from fatigue.
4: mild fatigue; impairment possible but not significant.
5: moderate fatigue; flying permissible but not recommended unless urgent.
6: severe fatigue; impairment probable; flying not recommended.
7: performance definitely impaired; flying not recommended.

These were working hypotheses for flight crews, not tested limits. On this site the rating is a way to track how your own shifts feel over time.

Common questions

Is the Samn-Perelli scale the same as the Karolinska Sleepiness Scale?: No. Samn-Perelli asks how tired you feel, on 7 points, while the Karolinska Sleepiness Scale asks how sleepy you feel, on 9 points. The 2025 airline study above used both.
Is a higher score better or worse?: Worse. 1 is fully alert and 7 is completely exhausted, so the number rises with fatigue.
Where does the name come from?: It is named for the two authors of the 1982 report, written at the US Air Force School of Aerospace Medicine at Brooks Air Force Base, Texas.

See your own shifts this way.

Bring in your schedule from any scheduling app with its calendar link. Capillary charts your hours, nights, quick returns and hardest shifts. Only you can see it.

Create an account Learn more