Quick Reference (Numbers to Remember)

Typography

• Body text: 16 px min, 18–20 px comfortable.
• Line length: 45–75 characters.
• Line height: 1.4–1.8; headings tighter.

Contrast

• Text: 4.5:1 (normal), 3:1 (large).
• Non-text UI: 3:1.

Motion

• Micro-interactions: 150–250 ms; entrances 200–300 ms.
• Respect prefers-reduced-motion; provide non-motion alternatives.

Touch targets

• 44×44 pt (iOS), 48×48 dp (Android) with 8–12 px spacing.

Timing

• Perceived instant: ~100 ms; flow: ~1 s; needs progress: ~10 s.

Memory

• Working memory practical capacity: 3–4 chunks.

Hearing

• Speech band: ~300–3400 Hz; safe continuous <85 dB.

References

• WCAG 2.2 Contrast: https://www.w3.org/WAI/WCAG22/Understanding/contrast-minimum
• Apple HIG — Touch targets: https://developer.apple.com/design/human-interface-guidelines/buttons#Size-and-layout
• NN/g — Response Times: The 3 Important Limits: https://www.nngroup.com/articles/response-times-3-important-limits/
• Cowan (2001) — Working memory capacity: https://en.wikipedia.org/wiki/Working_memory#Capacity