What is SFD?

Spline Font Database (SFD) is the native project file format for FontForge, an open-source font editor for font design.

What is AFM?

Adobe Font Metrics (AFM) is a text file describing Type 1 font metrics including character widths, kerning pairs, and bounding boxes.

When Should You Use SFD vs AFM?

SFD vs AFM: Key Differences

• •The core technical difference: SFD relies on lossless compression whereas AFM uses lossless compression.
• •Neither format changes compression philosophy — both are lossless compression — so any size differences are due to encoding efficiency, not a shift in quality approach.
• •Transparency: N/A
• •File sizes: SFD files typically range Larger than production fonts due to editing metadata and AFM files Very small, text-based metrics.
• •Use case fit: SFD targets font design and editing, fontforge projects and AFM targets postscript font metrics, pdf font embedding — your choice depends on which workflow stage you are serving.

Advantages of SFD

• ✓At its core, SFD relies on lossless encoding — a design choice that makes it perfect for Font design and editing, FontForge projects.
• ✓You won't run into compatibility issues with SFD — it's a universal standard across platforms.
• ✓File size management with SFD: larger files guaranteed to match the original exactly.
• ✓Every major application in the Font design and editing, FontForge projects space supports SFD natively.

Advantages of AFM

• ✓AFM applies lossless compression specifically calibrated for PostScript font metrics, PDF font embedding.
• ✓AFM enjoys broad native support across operating systems, browsers, and creative tools alike.
• ✓AFM guarantees every bit of the original data survives — no approximations, no shortcuts.
• ✓You will find AFM support built into virtually every tool that handles PostScript font metrics, PDF font embedding — no plugins or converters needed.

Common Use Cases for SFD to AFM Conversion

• Desktop publishing
• E-book formatting
• User interfaces
• Marketing materials
• Packaging design
• Signage systems

Industry Applications

Best Practices for SFD to AFM Conversion

• →Before converting SFD to AFM, review the font license — some licenses restrict format conversion
• →Check hinting data after conversion: AFM may handle TrueType hinting differently than SFD
• →Verify that all character sets (Latin, Cyrillic, CJK, etc.) survived the conversion intact
• →Test the converted font in both a browser and a desktop application
• →Keep the original font file in case the conversion alters spacing metrics

Troubleshooting SFD to AFM Conversion

• !AFM font doesn't render correctly → check if AFM supports all glyphs present in SFD
• !Licensing restrictions after SFD to AFM conversion → verify the font license allows format conversion
• !Hinting data lost converting SFD to AFM → some font formats like AFM may not preserve TrueType hinting
• !Special characters missing from converted AFM → font subsetting may have removed unused glyphs

Related Font Converters

All Font Formats

More Font tools