Shortcut takeaway: Treat 24 × 24 CSS px as the floor a standard requires, and the platform figures as the size to design to. SGDS's Button page states no minimum of its own. For a Singapore government web service, the WCAG figure is the one you are held to.
Squares are drawn at 1 unit = 1 CSS px. CSS px, pt and dp are each platform's density-independent unit, so the sizes are comparable but not identical on a given device.
These sources do not carry equal weight
- Standard requirement.
- A testable criterion in a published standard. Whether it is legally required depends on your jurisdiction and contract.
- Government control.
- A control the issuing government expects its agencies and their partners to apply. It does not bind other organisations.
- Design-system convention.
- How one design system does it. Binding only on teams that have adopted that system.
- Research-based best practice.
- Advice drawn from usability research. Persuasive, not mandatory.
- Industry convention.
- A range many shipping products use. Written by Shortcut; no standard or organisation requires it.
- Craft guidance.
- Judgement of the kind given in design review. Written by Shortcut; reasonable designers may disagree.