The time it takes to reach a target depends on how far away it is and how big it is. Large, nearby targets are fast and easy to hit; small, distant ones are slow and error-prone.
Overview
Every click, tap, and touch is a small physical movement, and some movements are harder than others. Fitts’ Law describes this precisely: the farther away and the smaller a target, the longer it takes to reach it accurately.[1][2]
The relationship is not linear. Doubling a target’s size or halving its distance makes it noticeably easier, but the benefit diminishes as targets get very large or very close. The law has been confirmed across mice, trackpads, touchscreens, and even eye-tracking and virtual reality.[3]
An interesting consequence is that screen edges and corners are especially easy to hit with a mouse, because the cursor stops at the edge. That is why many operating systems place important menus there.
Why it matters
Small or poorly placed targets slow people down and cause mis-clicks, especially on touch devices, for people with motor impairments, and for anyone working quickly. Over thousands of interactions, these small costs add up to lost time and avoidable errors.
Target size is also an accessibility requirement. WCAG 2.2 requires interactive targets to be at least 24 by 24 CSS pixels (with some exceptions), and recommends 44 by 44 pixels for enhanced accessibility.[4][5]
Key takeaways
- Make frequent and important targets large. Primary buttons should be easy to hit without precision.
- Place related actions close to where attention already is, such as next to the content they affect.
- Give touch targets enough size and spacing. Fingers are less precise than cursors.
- Make the whole element clickable. Labels for checkboxes and radio buttons, entire table rows, and full cards should respond, not just a small icon or word.
- Separate destructive actions from frequent ones so they are not hit by accident.
- Use edges and corners wisely on desktop for persistent, important controls.
In practice
Common patterns in business applications, portals, and internal tools:
Supports the principle | Undermines the principle |
|---|---|
Clicking a checkbox’s label toggles the checkbox. | Only the tiny box itself responds to clicks. |
Primary actions are large buttons near the end of the task flow. | Small text links for the main action, far from where the task ends. |
Touch targets meet or exceed accessibility minimums, with spacing between them. | Tiny icons packed tightly together on mobile. |
“Delete” is placed apart from “Save” and styled differently. | Destructive and primary actions side by side with identical styling. |
Context menus and inline actions appear near the selected item. | Actions only available in a toolbar on the opposite side of the screen. |
Questions to ask in a design review
- Are the most frequent actions on this screen also the easiest to reach and hit?
- Do all interactive targets meet minimum size requirements, especially on touch devices?
- Could a quick or imprecise click hit the wrong thing?
- How far does the pointer have to travel to complete the most common task?
Origin
Psychologist Paul Fitts published the law in 1954 after experiments in which people tapped back and forth between targets of different sizes and distances. He found movement time could be predicted mathematically from the ratio of distance to target width.[6]
In 1978, Stuart Card, William English, and Betty Burr at Xerox PARC used Fitts’ Law to compare pointing devices and found the mouse was fastest, research that helped establish the mouse as the standard pointing device.[7] I. Scott MacKenzie‘s 1992 review brought the law firmly into human-computer interaction.[3]
Related concepts
- Accot-Zhai Steering Law — an extension of Fitts’ Law for moving along paths
- Hick’s Law — the time to decide, rather than the time to move
- Mapping — placing controls near what they affect
- Affordances — targets must also look clickable
- Constraints — spacing prevents accidental actions
- Principle of Least Effort — people favor the easiest path
References and further reading
- Nielsen Norman Group. Fitts’s Law and Its Applications in UX. https://www.nngroup.com/articles/fitts-law/
- Yablonski, J. Fitts’s Law. Laws of UX. https://lawsofux.com/fittss-law/
- MacKenzie, I. S. (1992). Fitts’ Law as a Research and Design Tool in Human-Computer Interaction. Human-Computer Interaction, 7(1). https://doi.org/10.1207/s15327051hci0701_3
- W3C. Understanding WCAG 2.2 Success Criterion 2.5.8: Target Size (Minimum). https://www.w3.org/WAI/WCAG22/Understanding/target-size-minimum.html
- W3C. Understanding WCAG 2.2 Success Criterion 2.5.5: Target Size (Enhanced). https://www.w3.org/WAI/WCAG22/Understanding/target-size-enhanced.html
- Fitts, P. M. (1954). The Information Capacity of the Human Motor System in Controlling the Amplitude of Movement. Journal of Experimental Psychology, 47(6). https://doi.org/10.1037/h0055392
- Card, S. K., English, W. K., and Burr, B. J. (1978). Evaluation of Mouse, Rate-Controlled Isometric Joystick, Step Keys, and Text Keys for Text Selection on a CRT. Ergonomics, 21(8). https://doi.org/10.1080/00140137808931762
- Wikipedia. Fitts’s Law. https://en.wikipedia.org/wiki/Fitts%27s_law
- Yablonski, J. Laws of UX (format inspiration for this series). https://lawsofux.com/