We generally observe that a few actions on an app are easier to perform than others. In 1954, Paul Fitts, a psychologist, derived a mathematical principle to explain this scenario.
- T is the time taken to move to a target
- D is the distance of the target
- W is the width of the target
Fitt’s law suggests that the time taken to move a cursor to the target is:
- Directly proportional to the width of the target: the bigger the target, the better it is
- Inversely proportional to the distance of the target: the closer the target, the better it is
The law also implies that the actions placed at the edge of the screen are easy to reach and click. By utilizing Fitt's Law, Product Managers can build more user-friendly and easy-to-navigate interfaces. Few examples of where Fitt’s Law is utilized in the app we use daily:
Example #1: Google’s Material Design and Apple’s User Interface Guidelines
The user interface guidelines of Google and Apple suggest the designers keep the touch/click target size and distance between the two targets judiciously, allowing users to efficiently click on icons using their thumb. This would help in increasing the ease of clicking and reducing user errors due to wrong clicks.
Example #2: Forms
- The click area for inputting each field has an end-to-end or half-screen width, making it easy for users to click and fill in the information.
- The ‘Save’ button is at the edge, nearby the thumb, and has end-to-end width for a good clickable area.
Example #3: Menus
- In most of the apps, menu options and other important actions are placed at the edges of the screen to make it easy to locate and click them.
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Resources to learn how to improve usability using psychology principles
- Don't Make Me Think by Steve Krug (Paperback)
- Seductive Interaction Design by Stephen Anderson (Kindle | Paperback)
- Laws of UX by Jon Yablonski (Kindle | Audiobook | Paperback)