Tamaño mínimo de los elementos de interacción

Web Content Accessibility Guidelines (WCAG) 2.1 tiene el criterio 2.5.5 Target Size (Level AAA):

The size of the target for pointer inputs is at least 44 by 44 CSS pixels except when:

• Equivalent: The target is available through an equivalent link or control on the same page that is at least 44 by 44 CSS pixels;
• Inline: The target is in a sentence or block of text;
• User Agent Control: The size of the target is determined by the user agent and is not modified by the author;
• Essential: A particular presentation of the target is essential to the information being conveyed.

Además, Web Content Accessibility Guidelines (WCAG) 2.2, que todavía está en el estado Candidate Recommendation Draft, incluye nueve nuevos criterios. Uno de ellos es 2.5.8 Target Size (Minimum) (Level AA):

The size of the target for pointer inputs is at least 24 by 24 CSS pixels, except where:

• Spacing: The target does not overlap any other target and has a target offset of at least 24 CSS pixels to every adjacent target;
• Equivalent: The function can be achieved through a different control on the same page that meets this criterion.
• Inline: The target is in a sentence, or is in a bulleted or numbered list, or its size is otherwise constrained by the line-height of non-target text;
• User agent control: The size of the target is determined by the user agent and is not modified by the author;
• Essential: A particular presentation of the target is essential or is legally required for the information being conveyed;

En Accessible Target Sizes Cheatsheet aclaran todo esto con varios ejemplos.