Interface Design: Fitts’s Law
When we build applications, our primary mission is to support the activity at hand, whether it’s data analysis, data entry, or something else. Our design efforts center around questions like “What data does a person need to see on this screen? How should it be organized?” Besides merely enabling an activity, however, we want to deliver a friendly and easy interface. One of the ways we do that is by thinking about Fitts’s Law.
According to Fitts’s Law, the time it takes to move to a target is a function of the distance to and size of the target: time increases with greater distance, but decreases with greater size. In interface design, we apply the law when we make decisions about the size and location of objects on a screen: a bigger, closer button is easier to reach, while a smaller, more distant button will take more time to click. It’s not really that surprising, but it’s important enough that it’s always worth thinking about when designing an interactive interface (it’s often overlooked).
How do we apply Fitts’s Law when designing screens? Things that are clicked most frequently should be the easiest to reach. For example, in the survey design tool we recently built, the most frequently used object is the “Add a Question” button. It’s about this big:
There is, of course, a trade-off between object size and screen real estate. Not everything can be big, so we make the less important stuff smaller. But there are ways to make the “target” larger without actually taking up more screen space. For example, consider the difference between these two closing sentences:
Click here to see what the Nielsen Norman Group has to say about Fitts’s Law. You can also read more about Fitts’s Law on Wikipedia.