Tap Lab / Fitts's law

Shrink a button from 44 px to 16 px. How much slower are you?

Accessibility rules say a tap target should be at least 24 px, ideally 44 px. Guess what that costs, then tap 36 targets and get your own number.

1 / GUESS

You alternate between two bars, as fast as you can. How much longer does a tap take on a 16 px bar than on a 44 px bar?

+50%

Slide to your guess, then start.

2 / TAP
Block 1 of 4Width: -Taps: 0Misses: 0
Tap the highlighted bar. It switches sides each time.

A miss does not move the target; you have to hit it, so misses cost time. Works with mouse or finger.

3 / RESULT

Your time against difficulty

Each dot is one bar width. The line is your own fit of MT = a + b x ID, where ID = log2(D/W + 1) (the Shannon form used in ISO 9241-9).

Where the standards draw the line

WCAG 2.2 requires pointer targets of at least 24 by 24 CSS pixels (level AA, with spacing exceptions) and recommends 44 by 44 (level AAA). Your four test widths are 16, 24, 44 and 72 px, so one sits below the minimum, one exactly on it, one at the enhanced size and one above it.

Caveat: this is a quick one-axis test on your own device and pointer; four conditions give a rough fit, not a lab measurement.

Sources (opened this session): Fitts's law, Wikipedia (Shannon formulation ID = log2(D/W + 1), MT = a + b x ID, throughput; cites Fitts 1954, MacKenzie 1992, ISO 9241-9); WCAG 2.2 Target Size (Minimum) and Target Size (Enhanced) (24 and 44 CSS pixels).