NASA-TLX
NASA Task Load Index · Also known as: Task Load Index, TLX, NASA-TLX
The NASA Task Load Index (TLX) is a multi-dimensional subjective workload assessment tool developed at NASA Ames Research Center by Sandra Hart and Lowell Staveland in the 1980s. TLX measures perceived mental workload across six dimensions—mental demand, physical demand, temporal demand, performance, effort, and frustration—allowing researchers and practitioners to understand the cognitive and affective burden of tasks and interfaces. The instrument is widely used in human factors, cognitive engineering, and HCI to identify task bottlenecks and evaluate system designs.
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When to use it
Administer TLX after task completion, when users can reflect on the cognitive demands they experienced. Ideal for comparing competing designs, evaluating interface changes, or investigating how task characteristics affect workload. Best for complex, cognitively demanding tasks. Do not use for simple, routine tasks where workload differences may be small; SUS may be more appropriate for quick usability assessment.
Strengths & limitations
- Captures multiple dimensions of workload, providing diagnostic insights into which aspects of a task are most demanding.
- Validated across diverse domains (aviation, surgery, software use, driving) with extensive normative data.
- Sensitive to task and interface differences; small changes in complexity register reliably.
- Provides both overall workload score and dimension-level profiles for targeted improvement.
- Requires 10–15 minutes to administer and score (weighted version); more burdensome than SUS or brief scales.
- Subjective post-task rating; does not directly measure objective task difficulty or cognitive load.
- Sensitive to task context and individual differences; comparison across studies requires careful control.
- Weighted calculation requires pairwise comparisons, adding time and complexity; unweighted version simpler but less diagnostically rich.
Frequently asked
Should I use the weighted or unweighted version of TLX?
Weighted TLX is more sensitive and provides individual dimension importance. Use weighted for detailed analysis and smaller samples. Unweighted is faster (eliminates pairwise comparisons) and simpler to communicate; use for quick comparisons or when quick turnaround is critical.
What is a typical TLX score for a well-designed interface?
There is no single benchmark; TLX is relative to task complexity. Simple interfaces (web browsing) might score 20–40; complex tasks (surgical planning) 60–80. Use historical data from your own research or published norms for similar tasks as reference points.
Can I administer TLX during a task rather than after?
Not recommended. Real-time workload assessment interrupts the task. TLX is designed for post-task reflection. If you need continuous workload data, use objective measures (eye tracking, response time) or alternate real-time assessment tools like instantaneous self-assessment (ISA).
Sources
- Hart, S. G., & Staveland, L. E. (1988). Development of NASA-TLX (Task Load Index): Results of empirical and theoretical research. In P. A. Hancock & N. Meshkati (Eds.), Human Mental Workload (pp. 139–183). Elsevier. DOI: 10.1016/S0166-4115(08)62386-9 ↗
- Hart, S. G. (1986). NASA Task Load Index. Moffett Field, CA: NASA Ames Research Center. link ↗
How to cite this page
ScholarGate. (2026, June 3). NASA Task Load Index. ScholarGate. https://scholargate.app/en/human-computer-interaction/nasa-tlx
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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