UI Component Typography

UI component typography

Interface text is scanned and acted on, not read continuously. Different failure modes from body copy, and different rules.

1. When to invoke

• Typography inside buttons, labels, inputs, nav, tables, badges, tooltips.
• Numbers misaligning or jittering in tables or dashboards.
• Labels wrapping, truncating, or overflowing.
• Dense product UI where vertical space is contested.

Do not invoke for running prose (body-text-and-reading) or editorial layout (editorial-web-typography).

2. Required context

• The densest screen the component appears on.
• Longest realistic string for every label — in every supported language.
• Whether text is user-generated (unbounded length).
• Whether numbers are compared vertically (tables, ledgers) or read singly.
• Touch vs. pointer, and the minimum touch target.
• Whether the platform provides Dynamic Type / OS text scaling.

3. Invariant principles

• UI text is scanned, not read. Optimise for recognition speed and unambiguity, not reading comfort over long passages.
• Tabular figures are mandatory wherever numbers align vertically. Proportional figures have varying widths, so digits won't form columns. Lining + tabular is the combination for tables. (Lupton, Hochuli, Santa Maria)
• 1 l I and 0 O must be distinguishable in any interface showing codes, IDs, quantities, or currency.
• Every label must survive its longest translation. German and Finnish routinely run 30–40% longer than English.
• A label is not a placeholder. Placeholder-as-label disappears on focus and usually fails contrast.
• Text must survive the WCAG 1.4.12 spacing override — dense components are where this breaks first.
• Truncation is a last resort and must be recoverable — never truncate the only copy of information without a way to see it.

4. Context-dependent heuristics

Sizing. UI text usually runs smaller than body copy because it's scanned, not read — but small type raises the cost of a poor typeface. At 12–14px, aperture and counter behavior matter more than at 16px. Prefer a face with open apertures and a generous x-height for UI (see typeface-anatomy). Don't drop below ~12px for anything carrying meaning; never for anything a user must act on.

Line-height in components. Tighter than body text — a single-line label doesn't need 1.5. Around 1.2–1.35 for single-line UI strings, but note this is component line-height, not the paragraph rule. Any multi-line text inside a component reverts to body-text logic. WCAG 1.4.12 still requires the layout to survive a 1.5 override.

Figure styles — the four combinations.

.table-numeric { font-variant-numeric: tabular-nums lining-nums; }
.prose         { font-variant-numeric: oldstyle-nums proportional-nums; }

Full tag/property lookup in ../type/references/opentype-features.md.

Lining figures are usually cap height or slightly less and are normally set on a constant (en) body, which is what makes them tabular-capable (Hochuli).

Multiplexed typefaces solve the hover-reflow problem. In most families a heavier weight is also wider, so bolding a nav item or a tab on hover shifts everything after it. A multiplexed face is designed so every weight occupies exactly the same horizontal space — "a word set in a light weight will take up the exact same horizontal space as a word set in a heavy weight" (Stocks §31). Nothing moves.

Where a multiplexed face isn't available, the alternatives in order:

1. A variable font's GRAD (grade) axis — changes apparent weight without changing width. See variable-fonts.
2. Reserve the bold width up front (render the bold string invisibly to size the container, or set min-width).
3. Signal the state with something other than weight — colour, an underline, a background.

Never let a hover state reflow a navigation bar.

Labels and truncation. Design for the longest string first. Options, in order of preference: allow wrapping; allow the container to grow; shorten the copy; truncate with the full value available on hover/focus/detail. Truncating by default because the design assumed English is a localisation bug.

Alignment in tables. Numbers right-aligned (or decimal-aligned) so magnitudes compare; text left-aligned for a familiar entry point into reading; a column of icons or single glyphs centered, to avoid the lopsided look a left or right rag gives a symbol column. Headers match their column's data alignment. (Lupton, Type on Screen)

Case. Use text-transform: uppercase rather than typing capitals, so screen readers, search, and translation receive the real string. Add tracking whenever you do — see microtypography.

5. Failure patterns

6. Evaluation procedure

1. Render each component with its longest realistic string in the longest supported locale.
2. Render with the shortest string too — components often break empty.
3. In any table: confirm tabular-nums, and confirm numeric columns align.
4. Check 1 l I / 0 O in the shipping face at the shipping size.
5. Apply the WCAG 1.4.12 override; confirm nothing clips or overlaps.
6. Zoom to 200%; confirm no loss of content or function.
7. Check contrast for every state — placeholder, disabled, hover, error.
8. Confirm touch targets meet minimum size independent of text size.
9. Check any truncation has a recovery path.

7. Output format

Component: <name>
Size/line-height: <n>/<n> — rationale: <scan vs read, density>
Figures: <lining|oldstyle> + <tabular|proportional> — because <alignment need>
Longest string tested: "<string>" (<locale>) — <fits|wraps|truncates>
Digit disambiguation: <1lI ok?> <0O ok?>
1.4.12 override: <pass/fail> · 200% zoom: <pass/fail>
Contrast by state: default <n> · placeholder <n> · disabled <n> · error <n>
Truncation: <none|recoverable via …>

8. Examples

Dashboard table where "the numbers look wobbly".

The face defaults to proportional figures, so 1 is narrower than 8 and the digits don't form columns — the wobble is real, not perceptual. Fix is font-variant-numeric: tabular-nums lining-nums on numeric cells plus right-alignment so magnitudes compare down the column. Verified the face actually ships a tnum set (some don't, in which case the fallback is a monospace numeric face for those cells).

Primary button breaking in German.

"Save changes" → "Änderungen speichern" is 22 characters vs 12. The button has a fixed width sized to English, so the German string truncates. Fix in order: remove the fixed width and let the button size to content with a min-width; allow two-line wrapping with a tighter component line-height; only then consider shorter copy. Verified at 200% zoom and under the 1.4.12 override — with the fixed width removed, both pass.

9. Counterexamples

• ❌ "Use the placeholder as the label to save space." — Disappears on input, usually fails contrast, and breaks screen-reader association.
• ❌ "Set the button width so the layout stays consistent." — Guarantees a localisation failure.
• ❌ "Body line-height is 1.5, so use 1.5 everywhere." — Single-line UI labels don't need paragraph leading; but the layout must still survive a 1.5 override.
• ❌ "Numbers are fine, the font looks aligned." — Verify tabular-nums explicitly; proportional figures can look aligned in one sample and drift in another.
• ❌ "Truncate with an ellipsis, users can guess." — Truncation without recovery destroys information.
• ❌ Typing SUBMIT in the source to get uppercase. — Use text-transform.
• ❌ "10px is fine for secondary labels." — If it carries meaning, it must be legible.

10. Source citations

• Lupton, Thinking with Type 3e — the four figure styles: lining numerals uniform in height and resembling capitals; oldstyle/nonlining resembling lowercase with ascenders and descenders; tabular with uniform widths "ideal for tables and charts"; proportional with varying widths; lining and nonlining can each be tabular or proportional.
• Hochuli, Detail in Typography — lining figures usually cap height or slightly less, normally set on a constant (en) body so they can serve as tabular figures.
• Santa Maria, On Web Typography — tabular figures keep numbers lined up in vertical columns, making tables and spreadsheets easier to scan.
• Rutter, Web Typography — OpenType figure features; numerals and data tables.
• Lupton (ed.), Type on Screen — typography and data display; designing data tables; typography in interfaces.
• Brown, Flexible Typesetting — calibrated type for scanning complex information: tabular data, navigation, infographics, code.
• WCAG 2.2 §1.4.3, §1.4.4, §1.4.12.
• MDN — font-variant-numeric.