How do I calculate optimal web font file sizes?

Aim for under 50KB per font file. Calculate: original size → WOFF2 compression (60-70% reduction) → subsetting (70-90% reduction). A 200KB TTF can become 15-25KB WOFF2 subset.

What's the relationship between font size and load time?

Every 50KB of fonts adds approximately 100-200ms to page load on 3G connections. Reducing from 200KB to 50KB can improve LCP by 300-600ms on mobile.

How many glyphs does a typical Latin font need?

Basic English needs ~100 glyphs. Western European needs ~300. Full Latin Extended needs ~600. Most fonts include 2,000-10,000 glyphs; subsetting removes 70-95% of unused characters.

Should I calculate font budget per page or entire site?

Calculate per page for initial load. After first page, fonts are cached. Budget 100-150KB total for fonts on first page load, ideally split across 2-3 files.

How do variable fonts affect file size calculations?

A variable font is larger than one static weight but smaller than 3+ static weights. Break-even is typically around 3 weights. If you need 4+ weights, variable fonts save size.

Font Size Calculator

Calculate the performance impact of your font files. Estimate load times across different connection speeds and get actionable optimization recommendations.

Add each font file with its size in KB, select a connection speed (3G, 4G, or broadband), and the calculator estimates total download time, shows whether you are within a performance budget, and generates specific optimization recommendations. Results include per-font breakdowns and a pass/fail assessment against the 200 KB threshold recommended for good Largest Contentful Paint scores. Oversized fonts also contribute to render blocking, so use this calculator alongside the render blocking guide to prioritize which fonts to optimize first. Translating your optimized size targets into valid CSS @font-face declarations is covered in the CSS font implementation guide.

Your Fonts

Connection Speed

Total Size

53 KB

Budget: 100-200KB

Est. Load Time

0.15s

On 4G/LTE

HTTP Requests

Font files

LCP Impact

~122ms

Estimated delay

Optimization Recommendations

Ensure all fonts are in WOFF2 format for 30% size reduction.

Developer & Verifier

Developed by

Marcus Rodriguez

Full-stack developer specializing in web font implementation and performance optimization

Verified by

Sarah Mitchell

Typography expert specializing in font design, web typography, and accessibility

Typical Font Sizes Reference

Font Type	WOFF2 Size	Notes
Latin subset (single weight)	15-25 KB	English-only sites
Full Latin Extended	30-50 KB	European languages
Variable font (1 axis)	80-120 KB	Replaces 4-6 static files
Icon font	10-30 KB	Depends on glyph count
CJK (Chinese/Japanese/Korean)	500-5000 KB	Needs aggressive subsetting

In this article

How to Use This Calculator

Add Your Fonts

Enter each font file you load on your page with its size in KB. Check your build output or browser DevTools for actual sizes.

Select Connection

Choose a connection speed to simulate. 3G helps understand mobile user experience, while 4G represents typical conditions.

Review Results

Check if you are within budget and review recommendations. Target under 200KB total for good performance.

Font Performance Budgets

<100KB

Excellent

Minimal impact on LCP

100-200KB

Good

Acceptable for most sites

200-300KB

Needs Work

Consider optimization

>300KB

Poor

Significant LCP impact

Optimization Strategies

Subset Your Fonts

Remove unused characters to reduce file sizes by 50-90%. English-only sites rarely need full Unicode coverage.

Use Font Subsetter →

Use Variable Fonts

Replace 4-6 static weight files with a single variable font file. Often smaller total size and single HTTP request.

Learn About Variable Fonts →

Convert to WOFF2

WOFF2 provides 30% better compression than WOFF. Always serve WOFF2 as the primary format.

Convert to WOFF2 →

Reduce Font Weights

Many sites only need 2-3 weights (regular, medium, bold). Remove unused weights to cut file size. When adjusting type scales, use the font size converter tool to translate pixel values into rem and em units for a consistent, accessible type system. Minimum readable sizes also have accessibility implications; the font size accessibility requirements guide covers WCAG thresholds and recommended minimums.

Written & Verified by

Sarah Mitchell

Typography expert specializing in font design, web typography, and accessibility