Sift

Source Sans Pro

by Paul D. Hunt (Adobe) ★★★★☆ Sans-serif Variable Font
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Quick Answer

Source Sans Pro is a variable sans-serif font with 2 adjustable axes (Weight, Italic). Adobe's first open-source font family. Designed for UI with excellent readability.

Performance Impact

92%
Size Reduction
180 KB → 15 KB
-350ms
LCP Improvement
Core Web Vitals boost
12ms
4G Transfer Time
After optimization
100ms
Max Render Block
With font-display: swap

Download Time by Network

Slow 3G (400 Kbps) 300ms
vs ~3600ms unoptimized
Fast 3G (1.5 Mbps) 80ms
vs ~960ms unoptimized
4G LTE (10 Mbps) 12ms
vs ~144ms unoptimized

Optimization reduces Source Sans Pro from 180 KB to 15 KB — making your site faster on every device.

Try Source Sans Pro

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Variable Axes
400
200 900
0°
0 1
Loading Source Sans Pro...
Quick samples:

Variable Axes

Source Sans Pro includes 2 variable axes, giving you fine-grained control over the font's appearance.

wght

Weight

Controls weight from ExtraLight (200) to Black (900)

Range: 200 – 900 (default: 400)
ital

Italic

Toggles between upright and italic styles

Range: 0 – 1 (default: 0)

How to Optimize Source Sans Pro

1

Use Source Sans 3

The newer variable font version is more efficient than the static Source Sans Pro files.

Savings: 40-50%

2

Subset to Latin

Remove Cyrillic, Greek, and Vietnamese if not needed.

Savings: 55-65%

3

Convert to WOFF2

Essential compression for web delivery.

Savings: 30-40%

4

Use font-display: swap

Show fallback text while the font loads.

Savings: Performance

File Size Comparison

Source Sans 3 Variable (full)
~180 KB
All weights, all scripts
Source Sans 3 (Latin)
~55 KB
Latin subset only
Source Sans Pro Regular WOFF2
~20 KB
Single weight, Latin
Optimized with Sift
~15 KB
Subset + WOFF2

Sift optimizes your fonts for maximum performance with 90%+ size reduction

CSS Implementation

CSS
@font-face {
  font-family: 'Source Sans Pro';
  src: url('/source-sans-pro.woff2') format('woff2');
  font-display: swap;
  font-weight: 200 900;
}

body {
  font-family: 'Source Sans Pro', sans-serif;
}

For variable fonts, you can use font-variation-settings to control axes:

.custom-weight {
  font-variation-settings: "wght" 400, "ital" 0;
}

Pro Tips for Source Sans Pro

💡

Use the Source family

Pair with Source Serif Pro for body text and Source Code Pro for code to create a cohesive design system.

💡

Upgrade to Source Sans 3

The newer Source Sans 3 is a variable font and replaces the static Source Sans Pro.

💡

Excellent for UI

Source Sans was designed specifically for user interfaces, making it ideal for web apps.

💡

Adobe ecosystem

Matches Adobe product typography if designing for Adobe integrations.

Frequently Asked Questions

What is Source Sans Pro? ▼
Source Sans Pro was Adobe's first open-source typeface family, designed by Paul D. Hunt. It was developed for UI designers and has been optimized for excellent readability in both print and digital environments. The family includes matching serif (Source Serif) and monospace (Source Code Pro) companions.
Is Source Sans Pro a variable font? ▼
Yes, Source Sans Pro is a variable font with 2 axes: Weight, Italic. This means you can continuously adjust properties for precise control.
How do I optimize Source Sans Pro for web? ▼
To optimize Source Sans Pro: 1) Convert to WOFF2 format for smaller files, 2) Subset to only the characters you need, 3) Use font-display: swap to prevent invisible text, 4) Preload critical font files. Sift can automate this entire process.
What license does Source Sans Pro use? ▼
Source Sans Pro uses the SIL Open Font License 1.1 license.

Optimize Source Sans Pro Now

Convert to WOFF2, subset to Latin, and add font-display: swap in seconds.

Optimize Source Sans Pro