Enlarging target size and target spacing together

What it is

Touch adaptation for older users often gets reduced to "make the button bigger," but what actually determines the mis-tap rate is the combination of two variables: the size of the target itself, and the gap between it and its neighbors. Enlarging size alone while leaving the overall layout width unchanged can raise the mis-tap rate, because it squeezes neighboring targets closer together. Both have to be addressed together — doing only one does not count as done.

Why it happens

Mis-taps do not only come from "the finger is bigger than the target" — they also come from the landing point sitting too close to a neighboring target, so that a small positioning error lands on the wrong one. Enlarging a single target while holding the overall layout width fixed usually compresses the usable gap to its neighbors, offsetting or even outweighing the benefit of the larger size. That is why the intuitive fix of "make the button bigger" sometimes backfires: it looks more prominent visually while its clickable boundary now intrudes further into its neighbor's territory.

Where it stops holding

This adaptation runs directly into conflict with "how much can fit on one screen" in high-density, physically constrained contexts — smartwatches, certain zones of an in-car console — where size and spacing cannot simply be enlarged without limit; the answer there is a different interaction shape (progressive disclosure, voice input, layered navigation), not forcing oversized targets into a tight space. Not every older user has fine-motor control issues either — for users whose dexterity is unaffected, oversized targets simply lengthen the visual scan and travel distance, increasing task time.

Applying it

• Keep the minimum edge length of a touch target at roughly 9–10mm, taking the upper end of that range for contexts primarily used by older adults.
• Keep the gap between adjacent interactive targets at no less than about 2mm — size and spacing must both be met; satisfying only one does not count.
• Give frequent, higher-consequence actions (submit, delete, confirm payment) priority for a larger size-and-spacing budget; infrequent, low-consequence actions can be tighter.
• Verification: on a real device, tap through densely packed regions (a numeric keypad, a cluster of list-row action buttons) with a finger rather than a mouse or stylus, and count mis-taps on neighboring targets. Where possible, test with actual older participants holding the device naturally and without instructions to be extra careful, rather than team members deliberately tapping with care in a lab setting.

Related

• Same group: A11.03.1 minimum font size and user-adjustable text scaling · A11.03.7 debounce and mis-tap filtering for hand tremor
• Nearby: A8.15 physiological tremor · A11.06 anthropometric data and sizing
• Search terms: touch target size · target spacing · fat finger problem