Models and Theories in Human-Computer Interaction/Fitts' Law in Touch Screen Age

Fitts’ Law in Touch Screen Age.

Fitts’ law( Fitts, 1954) states that MT=a+ b × log2(D / W + 1). This formula deals with target size, movement time, target distance, etc. Those are all essential elements and aspects that should be considered in terms of the design of touch screen interfaces.

This law reminds me a project I did last semester in another HCI design class. I designed an interface for an iphone application. I didn’t realize the important of the size and position of the buttons until I did two user tests. I found that the farther the button away of the main part of this interface, the more difficult and more time consuming for testers to find this button; at the same time, if the button is too small for testers to click and touch, the error rate will be increase.

Then I did some research saying that the Apple’s iPhone Human Interface Guidelines recommends a minimum target size of 44 pixels wide 44 pixels tall [1]. Additionally, according to Landauer and Nachbar’s study, it us clear that there is a log linear relation that can be used to evaluate whether a keypad is successful or not based on participants’ performance [2].

In my opinion, Fitts’ Law can be a very valuable formula and ruler for touch screen interface design in terms of button size and position.


1. 2. T.K. Landauer and D.W.Nachbar. “Selection From Alphabetio and Numerio Menu Trees Using A Touch Screen: Breadth, Depth, and Width.” In CHI’ 85 Proceedings. April 1985. pp 74-75.