Typography Design Skill

When to Activate

• Choosing typefaces for a new product or brand
• Building a typographic scale (H1–body–caption)
• Critiquing readability or hierarchy problems
• Optimising for web and mobile rendering
• Defining letter-spacing and line-height ratios
• Evaluating a font pairing
• Selecting a modular scale ratio appropriate for the information density of a UI
• Diagnosing FOUT or FOIT issues and choosing the right font-display strategy for body vs. display fonts

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Typeface Selection Criteria

Evaluate every candidate font on five criteria before using it:

Criterion	What to check
Personality	Does the tone match the brand? (geometric = technical, humanist = friendly, slab = authoritative)
Rendering quality	Does it look good at screen sizes (12-18px)? Test hinting at small sizes.
Weight range	Minimum 4 weights needed: Light/Regular/Medium/Bold. Variable font preferred.
Character set	Does it support all required languages (Latin Extended, Cyrillic, Arabic)?
License	Free for web use? Requires self-hosting? Commercial license required?

Classification overview

Classification	Characteristics	Use for
Geometric sans	Circle-based O, uniform stroke	Tech, modern, minimal
Humanist sans	Variable stroke, organic	UI text, long-form, accessibility
Transitional serif	High contrast, bracketed serifs	Premium, editorial
Slab serif	Low contrast, block serifs	Authoritative, data-heavy
Display	Decorative, expressive	Headlines only, large sizes

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Typeface Pairing Rules

The contrast rule

Display and body must be from different classifications:

WORKS:
Geometric sans (display) + Humanist sans (body)
→ Space Grotesk + Inter

Serif (display) + Sans (body)
→ Playfair Display + Source Sans 3

Slab serif (display) + Clean sans (body)
→ Zilla Slab + Roboto

DOES NOT WORK:
Geometric sans + Geometric sans (both Inter-style: boring)
Two serifs (competing, no hierarchy)
Two display fonts (chaotic)

The harmony rule

Despite contrasting in classification, paired fonts should share proportions:

• Similar x-height (body height of lowercase letters)
• Compatible optical weight at the same px size
• Test by setting both at the same size — do they feel balanced?

Anti-patterns

• Both fonts are variable fonts of the same super-family — no contrast (e.g., Roboto + Roboto Condensed)
• Display font used for body text — decorative fonts are illegible at small sizes
• Three or more typefaces — almost always wrong; two is the limit

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Modular Scale

A modular scale generates all text sizes from a base size and a ratio. It creates visual harmony — sizes feel related rather than arbitrary.

Choosing a ratio

Ratio	Name	Character
1.067	Minor Second	Tight, minimal — good for data-dense UIs
1.125	Major Second	Subtle, professional
1.200	Minor Third	Balanced — good default
1.250	Major Third	Clear hierarchy
1.333	Perfect Fourth	Strong contrast — editorial
1.500	Perfect Fifth	Very bold — display-heavy

Calculating the scale (base 16px, ratio 1.25)

caption:    10.24px  (16 × 1.25⁻²)
small:      12.80px  (16 × 1.25⁻¹)
base:       16.00px  (16 × 1.25⁰)
large:      20.00px  (16 × 1.25¹)
h4:         25.00px  (16 × 1.25²)
h3:         31.25px  (16 × 1.25³)
h2:         39.06px  (16 × 1.25⁴)
h1:         48.83px  (16 × 1.25⁵)
display:    61.04px  (16 × 1.25⁶)

CSS custom properties

:root {
  --text-xs:   0.640rem;   /* 10.24px */
  --text-sm:   0.800rem;   /* 12.80px */
  --text-base: 1.000rem;   /* 16.00px */
  --text-lg:   1.250rem;   /* 20.00px */
  --text-xl:   1.563rem;   /* 25.00px */
  --text-2xl:  1.953rem;   /* 31.25px */
  --text-3xl:  2.441rem;   /* 39.06px */
  --text-4xl:  3.052rem;   /* 48.83px */
  --text-5xl:  3.815rem;   /* 61.04px */
}

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Spacing Ratios

Line height

Context	Line height	Why
Display / headlines	1.1–1.2	Tight — prevents gaps between lines at large sizes
Subheadings	1.2–1.3	—
Body text	1.5–1.7	Loose — aids readability at body sizes
Long-form (articles)	1.6–1.8	Maximum readability
UI labels, buttons	1.0–1.2	Single-line — no wrapping expected

Letter spacing (tracking)

Context	Tracking	Why
Headlines (32px+)	-0.02em to -0.04em	Tight — large letters feel too spaced at default
Body text	0 (default)	Never adjust body letter spacing
ALL CAPS / small caps	+0.05em to +0.12em	All-caps needs extra air
UI labels (12-14px)	+0.01em	Tiny text benefits from extra tracking

Paragraph spacing

• Paragraph spacing = 0.75–1× the base line height
• Never use double line breaks for paragraph spacing in production — use margin-bottom
• Tighter paragraph spacing for UI; looser for editorial / article layouts

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Hierarchy Construction

The three tools

Build hierarchy using these tools in priority order:

1. Size — most powerful; large type draws the eye first
2. Weight — second; bold vs. regular creates emphasis
3. Color — third; primary vs. secondary vs. disabled

Avoid using all three at once — it creates noise. One or two tools per level is enough.

Anti-patterns

• Too many sizes — if more than 5 distinct text sizes exist in a single viewport, something is wrong
• All bold — when everything is emphasized, nothing is
• Color only — low-contrast secondary text on colored backgrounds fails WCAG

H1–H6 specification template

H1 — 3.052rem / line-height 1.15 / weight 700 / tracking -0.02em
H2 — 2.441rem / line-height 1.20 / weight 700 / tracking -0.01em
H3 — 1.953rem / line-height 1.25 / weight 600 / tracking 0
H4 — 1.563rem / line-height 1.30 / weight 600 / tracking 0
Body large — 1.125rem / line-height 1.60 / weight 400
Body — 1.000rem / line-height 1.60 / weight 400
Body small — 0.875rem / line-height 1.50 / weight 400
Caption — 0.750rem / line-height 1.40 / weight 400 / tracking +0.01em

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Rendering Considerations

Variable fonts

Use variable fonts where possible — one file covers all weights, reducing HTTP requests:

@font-face {
  font-family: 'Inter';
  src: url('/fonts/Inter-Variable.woff2') format('woff2-variations');
  font-weight: 100 900;   /* entire weight axis */
  font-display: swap;
}

FOUT / FOIT strategy

• FOUT (Flash of Unstyled Text) — content visible immediately, swaps to web font
• FOIT (Flash of Invisible Text) — invisible until font loads

Use font-display: swap for body text (FOUT — content always readable). Use font-display: optional for decorative display fonts (skip if load is slow).

System font stack fallback

Define a fallback that matches the web font's character:

/* For sans-serif web font */
font-family: 'Inter', ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;

/* For serif web font */
font-family: 'Playfair Display', ui-serif, Georgia, 'Times New Roman', serif;

/* Mono */
font-family: 'JetBrains Mono', ui-monospace, 'Cascadia Code', 'Fira Code', monospace;

iOS vs. Android rendering

• iOS renders fonts at 1× sharper than Android at the same CSS px
• Android at small sizes may need +0.01em letter spacing for clarity
• Test at 12-14px on a physical Android device — system font fallbacks look very different

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Checklist

• Typeface evaluated on: personality, rendering, weight range, character set, license
• Pairing contrasts in classification (not two geometric sans)
• Paired fonts share similar x-height
• Modular scale chosen with ratio appropriate to the UI density
• Line height: 1.5-1.7 for body, 1.1-1.2 for headlines
• Negative tracking on headlines (32px+); never on body
• Positive tracking on all-caps text
• Hierarchy uses at most 2 of the 3 tools per level (size, weight, color)
• Maximum 5 distinct text sizes in a single viewport
• Variable font used where available
• font-display: swap on body text fonts
• System font fallback stack defined for each web font