Textbook of Usability

Hick's Law (also Hick–Hyman Law) predicts the time it takes for a person to make a decision as a function of the number of possible choices:

$$T = b \log_2 (n + 1)$$

where $T$ is decision time, $n$ is the number of equally probable alternatives, and $b$ is an empirical constant (typically around 150ms per bit for trained users).

Like Fitts's Law, the relationship is logarithmic: a menu with 16 items is only twice as slow as a menu with 4 items, not four times as slow.

Design implications:

• Menus should be organised hierarchically rather than as long flat lists
• Cognitive load can be reduced by chunking choices into categories
• Keyboard shortcuts bypass Hick's Law entirely (they're a fixed-time operation once memorised)
• Defaults speed up decisions by removing the need to choose at all

Hick's Law applies to deliberate choices among visible options. It does not apply to habitual responses or decisions involving complex tradeoffs.