Fitts’s Law

Would you believe that one of the most important fundamental and common sense laws of design is also one of the most frequently ignored? We can’t believe it either. You may or may not have heard of Fitz’s law, but if you’ve designed any interfaces, you’ve almost certainly used it. A researcher named Paul Fitz created a model that describes how quickly people can select a target. It’s important to know this law if you’re designing websites, mobile apps, device interfaces or even physical dashboards.

Fitz’s law says that the time to acquire a target is a function of the size of the target and the distance to the target. Here’s the equation. The important variables are the target and the distance to that target. A target is what the user is trying to interact with. Maybe it’s a button to tap or a form field that needs to be clicked into the distance to the target is how far away that target is from wherever someone starts out, large targets that are close by have the lowest interaction costs, while small targets that are far away have the highest interaction costs. Here are a few common applications of Fitzloff buttons to complete. An action should be close beside the active elements. Important actions should be larger so they’re easier to select with menus, drop downs and any type of interactive list. Shorter is better. This is a guideline rather than an absolute rule. Sometimes a list has to be long to show all of the options that users need to see. This seems like common sense, but it’s one of the most frequently ignored laws of design.

Remember that large targets and less time needed to find them keep interaction costs low.

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