A shaky hand: why small targets fail

Essential tremor is the most common movement disorder in adults. It affects about 1 person in 75¹ overall, and about 1 in 20 over the age of 65.

That is several times more people than have Parkinson’s disease, which the World Health Organization counted at more than 8.5 million² people in 2019, twice as many as 25 years before. Close to half of people with multiple sclerosis⁴ report a tremor. One American adult in five has arthritis, and cerebral palsy is the most common motor disability in childhood.

Then there is everyone else, some of the time: hands that are cold, tired, anxious or over-caffeinated, medicines from asthma inhalers to antidepressants, and phones used on trains and in cars. The accessibility guidelines name “vibrating environments” right beside hand tremors.

Essential tremor is an action tremor: it gets stronger when the hand is doing something, and aiming at a small button is exactly that.

It shakes four to twelve times a second. Parkinson’s tremor is different, strongest at rest and a little slower. Either way, a click lands where the hand happens to be at that instant, not where the person meant. A small target needs many attempts, and a target next to a destructive one is a trap.

Age changes pointing too, though perhaps not as people assume. One study found people in their sixties slower but not less accurate⁵ than younger adults: they get there, and it costs them more time and effort. A touchpad slowed them most of all.

The Web Content Accessibility Guidelines ask for targets of at least 24 by 24 pixels⁷, or smaller ones with enough space around them.

That is the minimum, level AA. The enhanced level asks for 44 by 44⁸, close to what Apple (44 points) and Google’s Material Design (48) recommend for touch. Links inside a sentence are exempt, which is one more reason to make the important actions proper buttons.

For thumbs, a study at the University of Maryland found errors stopped falling once targets reached about 9.6 millimetres⁶. For older people on touchscreens, researchers have suggested buttons of about 20 millimetres with a few millimetres between them.

This tool changes how your clicks and taps land, and it catches pointer presses as well as clicks, so it works on prototypes that are drawn as a picture, such as a Figma prototype link, as well as on live pages.

A few apps listen for presses in ways no bookmark can reach; if nothing changes when you click, the app is one of them.