NASA Task Load Index (NASA-TLX)
A 6-dimension subjective workload scale completed immediately after a task.
By Claire White
- Self-administered after completing a task; approximately 5 minutes.
- Six subscales: mental demand, physical demand, temporal demand, performance, effort, and frustration.
- Each subscale rated 0 to 100 in 5-point increments.
- Overall workload score is the unweighted mean of all six subscales (Raw TLX) or a weighted mean.
What does the NASA-TLX measure?
The NASA-TLX captures the subjective workload of completing a task. Immediately after the task, the person rates six dimensions.
| Dimension | What it asks |
|---|---|
| Mental demand | How much mental and perceptual activity the task required |
| Physical demand | How much physical activity the task required |
| Temporal demand | How much time pressure the person felt |
| Performance | How successful they judge themselves to have been |
| Effort | How hard they had to work to reach that level |
| Frustration | How irritated, stressed, or discouraged they felt |
In brain-computer interface and AAC research it is used to assess the cognitive and emotional burden of operating a communication interface.
What does a NASA-TLX score mean?
Higher scores mean higher subjective workload. There is no cutoff and no severity band, because the NASA-TLX is comparative by design: it tells you which of two interfaces, input methods, or protocols feels more demanding, and which of the six dimensions carries that load. A design change that lowers the overall score while raising frustration is telling you something a single number would hide.
The Raw TLX, the unweighted mean of the six subscales, is common in BCI research because it tracks the weighted version closely with less administration burden.
How the NASA-TLX is administered
- Completed by
- The person who performed the task, immediately afterwards
- Time to complete
- About 5 minutes
- Scoring
- Six ratings 0 to 100 in 5-point steps; weighted, or averaged as Raw TLX
- Weighting step
- 15 pairwise comparisons, omitted in the Raw TLX variant
- Cost
- Free to take here.
- Published by
- NASA
- Domain
- Human factors and ergonomics, not a clinical instrument
Related instruments
NASA-TLX questions, answered
How is the NASA-TLX scored?
Each of the six dimensions is rated on a 0 to 100 scale. In the original weighted version, the person also makes 15 pairwise comparisons between the dimensions, and those weights shape the overall score. Many studies skip the weighting and average the six ratings instead, which is called Raw TLX. The two approaches give very similar results.
What is a high NASA-TLX score?
There is no universal cutoff. The score is comparative. It shows which of two tasks, devices, or interface designs feels more demanding, and which dimensions carry the load.
What is the difference between NASA-TLX and Raw TLX?
Raw TLX drops the 15 pairwise weighting comparisons and averages the six dimension ratings. It is faster to administer and tracks the weighted score closely.
Where does the NASA-TLX questionnaire come from?
Hart and Staveland developed it at NASA Ames Research Center in the 1980s to measure workload in aviation, and it spread across human factors research from there. NASA distributes the paper version freely. The version here runs the six ratings online.
Evidence, psychometrics and provenance
Psychometrics
- Test-retest reliability
- Moderate to high across task types
- Construct validity
- Correlates with objective workload measures across many domains
References
- 1.Hart SG, Staveland LE. Development of NASA-TLX: results of empirical and theoretical research. In: Hancock PA, Meshkati N, eds. Human Mental Workload. Amsterdam: North-Holland; 1988:139-183.
This assessment uses a validated instrument and is reference information, not a diagnosis.