During a project for a Czech legal consultancy, we changed exactly one thing on their homepage: the body typeface. We swapped a narrow geometric sans-serif for a humanist one with slightly wider proportions and more open counters. Within the first month, average time on page climbed and bounce rates decreased. No layout changes, no new content, no restructured navigation — just a different font. Typography is often treated as a cosmetic detail, but it fundamentally shapes how people experience a website.
Fonts Shape User Perception
Type carries meaning before a single word is read. A serif typeface like Garamond suggests tradition and authority. A rounded sans-serif like Nunito feels approachable and friendly. A monospaced font like JetBrains Mono signals technical precision. These associations are deeply ingrained and culturally reinforced through decades of print and digital design.
Choosing the wrong typeface creates cognitive dissonance. We once audited a wellness brand's website that used an angular, industrial-looking sans-serif — the kind you might expect on a construction company's site. The content spoke of calm, balance, and self-care, but the typography contradicted every word. Aligning the typeface with the brand's personality was one of the simplest and most effective changes in that entire redesign.
The Magic of Readability
Readability is not just about font choice — it is about how text is set. Line length, line height, and letter spacing work together to create comfortable reading conditions. The widely cited ideal for body text is 50–75 characters per line, which translates to roughly 600–700 pixels of text width at standard body sizes on desktop screens.
Line height (or leading) should generally sit between 1.4 and 1.6 for body text, though the optimal value depends on the typeface's x-height and overall proportions. Fonts with tall x-heights, such as Inter or Source Sans Pro, can work well at 1.5 line height. Fonts with shorter x-heights, like Caslon or Baskerville, may need 1.6 or more to feel open and readable.
Contrast between text and background also plays a critical role. WCAG 2.1 requires a minimum contrast ratio of 4.5:1 for normal text, but we aim higher — typically 7:1 or above — because meeting the minimum standard does not always equate to comfortable reading, especially on mobile screens viewed in variable lighting conditions.
Picking the Right Font Size
The days of 12-pixel body text are long behind us. Modern best practices place body text at 16–18 pixels as a baseline, with many content-heavy sites pushing to 20 pixels. Larger body text improves readability on high-resolution displays and reduces the need for users to zoom.
We use a modular type scale to establish consistent sizing across headings, subheadings, body text, and captions. A ratio of 1.25 (major third) works well for most web projects, producing a hierarchy that feels balanced without dramatic jumps between sizes. For a site where headings need more visual impact, we might use a 1.333 (perfect fourth) or even 1.5 (perfect fifth) ratio.
Responsive type sizing is essential. We use CSS clamp() to create fluid typography that scales smoothly between breakpoints. For instance, font-size: clamp(1rem, 0.5rem + 1.5vw, 1.25rem) ensures body text remains proportional across screen sizes without abrupt shifts at specific breakpoints.
Font Pairing: Mix but Don't Overdo It
Pairing typefaces is one of the most nuanced decisions in web typography. The goal is contrast with harmony — two fonts that look distinct enough to create hierarchy but share enough structural similarity to feel cohesive. A classic approach pairs a serif heading font with a sans-serif body font, or vice versa.
We keep pairings to two typefaces per project in almost every case. Three is the absolute maximum, and only when there is a clear functional reason — for example, a monospaced font for code blocks alongside a serif/sans-serif pair for editorial content. Each additional typeface adds cognitive load for the reader and increases page weight from font file downloads.
When selecting pairs, we look at shared characteristics: similar x-heights, compatible stroke widths, and proportional letter widths. Fonts designed by the same foundry or type designer often pair well because they share underlying design principles. Playfair Display and Source Sans Pro, for example, have complementary proportions that create elegant contrast without visual tension.
The Right Choice Can Boost Conversions
Typography directly influences conversion rates because it affects comprehension and trust. When users can read content easily and the visual tone matches the brand's promise, they are more likely to take action. This applies to everything from call-to-action buttons to product descriptions to pricing tables.
For a SaaS client in the project management space, we tested two versions of their pricing page. The only difference was the typeface used for plan names and feature lists — one version used a neutral geometric sans-serif, the other used a slightly warmer humanist sans-serif with better readability at small sizes. The humanist variant performed better on plan selection because users could parse the feature comparisons more quickly and confidently.
Test and Iterate
Typography decisions should be validated, not assumed. We run readability tests with real users during the prototyping phase, asking them to read passages and answer comprehension questions. We also track engagement metrics after launch — time on page, scroll depth, and conversion rates — to measure whether typographic changes produce measurable outcomes.
A/B testing typefaces in production requires careful implementation. Font loading behavior affects perceived performance, and different fonts can shift layout in ways that confound test results. We use the CSS Font Loading API to ensure consistent rendering across variants and control for cumulative layout shift.
At Kosmoweb, typography is never an afterthought. It is one of the first decisions we make in any project because it shapes every subsequent design choice — spacing, layout, color, and hierarchy all flow from the type system. Getting it right early saves time and produces better results throughout the entire design process.