How to Import a Kerning Table in FontForge

Importing an external kerning table into FontForge allows you to quickly apply pair-spacing data from other fonts or metric generation tools without manually entering values. This guide explains how to import external metrics files, such as Adobe Font Metrics (.afm) or OpenType Feature files (.fea), directly into your FontForge project to update your font's kerning tables accurately.

Supported File Formats

FontForge primarily imports external kerning data through two file types:

  • Adobe Font Metrics (.afm): Standard text files containing character bounding boxes and horizontal kerning pair values (KPX records).
  • OpenType Feature Files (.fea): Syntax-based text files containing OpenType layout rules, including GPOS (Glyph Positioning) pair adjustment lookups.

Method 1: Using the "Merge Feature Info" Command

The most direct way to import kerning from an .afm, .tfm, or .fea file is by merging the feature information into your existing font.

  1. Open your font project in FontForge.
  2. Click on File in the top menu bar.
  3. Select Merge Feature Info....
  4. In the file browser, navigate to and select your external kerning file (.afm or .fea).
  5. Click Open.

FontForge will read the kerning pairs from the file and automatically populate the internal kerning subtable.

Method 2: Importing via Font Info (for OpenType Feature Files)

If your kerning data is structured inside an OpenType feature file (.fea), you can import it through the Font Info panel to ensure it is correctly mapped to a GPOS lookup table.

  1. Open your font in FontForge.
  2. Go to Element > Font Info (or press Ctrl+Shift+F / Cmd+Shift+F).
  3. In the left-hand sidebar, select Lookups.
  4. Click on the GPOS tab at the top of the window.
  5. Click the Add Lookup button, select Pair Adjustment (Kerning) as the lookup type, and assign it the kern feature tag. Click OK.
  6. Select the lookup or subtable, click Import, and select your .fea file.
  7. Click OK to apply the changes and close the Font Info window.

Verifying the Imported Kerning Data

To confirm that the external kerning pairs have loaded successfully:

  1. Click on Metrics in the main menu.
  2. Select New Metrics Window (or press Ctrl+K / Cmd+K).
  3. Type character combinations that should have kerning values (e.g., "AV", "To", or "WA").
  4. Check the Kern field between the glyphs at the bottom of the window to verify that the imported spacing offset is active.