Luke W’s article “Touch Target Sizes” gives helpful guidelines for designing touchscreen buttons. The button sizes listed there were collected from several sources, such as the iPhone Human Interface Guidelines, all linked from the article.

The guidelines and tips are really useful, for example when you work on a responsive web design. Designing buttons for a finger is a different task from designing buttons for a mouse.

Button sizes have to match the size of a fingertip, and the spacing between buttons should be generous so that nobody taps the wrong one by accident. Apple’s figure for a standard touchscreen button is 44 by 44 points. That seems very large at first, but one trick is to make only the tappable area that size and draw the visible button smaller.

Translated from the German original of 21 November 2011.