Selecting Finger Size:
Diameter of an adult finger is typically of 16mm to 20mm. Generally, for pushing buttons and using touch screen, finger pad is used. They are narrower than full finger but wider than the fingertip. The size of the finger pad is 10-14mm.

Image of a finger pad.


Image of a fingertip.

Fingertip is narrower than finger pad and full finger. The size of the fingertip is 8-10mm.

Calculating Target Size:
The interface element where user is asked to touch to select, should not be smaller than 1cm diameter or 1cm*1cm

• “Size of the target element = Target size in inches (0.4 inch) * Pixel per inch”
• “Pixel per inch (PPI) = Screen width in pixel/screen width in inch”

The higher the PPI, the larger your interface elements will have to be to create suitable touch targets