NASA-TLX

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NASA-TLX, the NASA Task Load Index, is a simple, subjective tool used to judge how demanding a task feels to a person. Developed at NASA Ames after a three-year project with more than 40 simulations, it helps researchers evaluate workload for a task, system, or team. It relies on people’s own ratings rather than objective measures like speed or accuracy.

The tool has two parts. Part 1 asks the user to rate six aspects of workload on a 0–100 scale in five-point steps: Mental Demand, Physical Demand, Temporal Demand, Performance, Effort, and Frustration. Brief descriptions help participants answer accurately. Part 2 asks the user to compare these six aspects in pairs to decide which are most important to workload. The number of times each aspect is chosen becomes its weight. The final score is a weighted combination of the six ratings, giving a NASA-TLX score from 0 to 100.

Some researchers use a shorter version called “Raw TLX” by skipping the weighing step or dropping less relevant subscales. This can be more valid for certain tasks. NASA offers an official paper-and-pencil version and an iOS app. There are many unofficial digital versions, some of which collect personal data, which can violate NASA guidelines. How TLX is administered can affect results: some studies find paper versions show lower perceived workload than computer versions, while others show computer or wearable versions still accurately track changes. The official iOS app includes SAER, a rating feature that closely mimics the paper experience and helps capture subjective input more accurately. Other digital versions often use fixed scales that can reduce the measure’s subjectivity.

In short, NASA-TLX is a popular, flexible way to measure perceived workload, but researchers should choose the right format and be mindful of potential biases and privacy when collecting data.