Fitts' Law Revisited
In 1954, psychologist Paul Fitts showed that the time required to move to a target depends on the distance to it and inversely related to its size. By his law, fast movements and small targets result in greater error rates, due to the speed-accuracy trade-off. Fitts' law is widely applied in user experience and user interface design. For example, this law influenced the convention of making interactive buttons large, especially on finger-operated mobile devices since smaller buttons are more difficult.
One of the most important lessons we can take from Fitts’ law is that, while a larger target is clearly easier to click on, it isn't necessarily the most optimal. This is counter to what many user interfaces do with their oversized user interface components. Bigger items aren't always better than smaller items in the Fitts’ Law.
Creating larger targets will facilitate interaction as well as allow you to get the most pixels out of your interface. The downside of large targets is that they can break the balance in our interface as well as take up screen real estate. Even if we have plenty of space to spare, we do not have to constantly enlarge our target areas to make them more usable since the predicted usability of the size of a button progresses in non-linear.
If we place the links and buttons where users are most likely to access them on a regular basis next to each other, rather than distribute them across the interface, we can speed up interaction by reducing the number of pixels the cursor will have to travel. But, arranging elements only according to this formula can cause conflict with other important design principles, such as the principle of grouping and separating different classes of functionality or content. Its purpose is to give our interface a clear and consistent structure as well as making it stand out.
The problems faced by UX designer for designing interfaces include considering the balance, combining the measurable and non-measurable dimensions of the usability and user experience to create the best fit for the users. Fitts' law provides designers a way of dealing with them in a quantifiable measure using the mathematical equations. This may lead designers to favor the measurable over not so easily measurable dimensions. And while mathematical formulas can help us enrich user experience, we should treat those formulas as guides, not as rules.