Hick's Law Reaction Time Calculator
Calculate choice reaction time from number of response alternatives using Hick's law.
Enter baseline RT, information processing rate, and number of choices to predict response speed.
Hick’s law (Hick-Hyman law), established in 1952, describes how reaction time grows with the number of equally likely choices. More options means more information to process, and processing takes time.
The formula:
RT = a + b x log2(n + 1)
where RT is reaction time in milliseconds, n is the number of equal-probability response alternatives, a is the base reaction time (minimum RT with no uncertainty, typically 100-200 ms), and b is the information processing rate (ms per bit, typically 100-200 ms/bit).
Why log base 2? Each doubling of choices adds exactly one bit of information. Going from 2 to 4 choices adds one bit. Going from 4 to 8 adds another. The brain processes this information at a roughly constant rate, so RT grows linearly with bits.
Typical parameter values:
- Simple reaction time (n=1): 150-250 ms
- a: 100-200 ms (varies by individual and modality)
- b: 150-200 ms/bit for finger responses
Applications outside psychology. UX designers use Hick’s law to justify limiting navigation menu items. Too many choices increases the time users take to decide. Martial artists use it to explain why technique libraries that are too large become a liability in a fight — scanning more options slows the response.
The law breaks down with practice. Expert chess players do not scan moves sequentially; they pattern-match to familiar positions and bypass the linear search. When response options are predictable, RT no longer follows the log2 relationship.