How to Define Kerning Pairs in FontForge

Adjusting kerning pairs manually in FontForge ensures that visually awkward character combinations, such as "AV" or "To," maintain balanced spacing across all text. This guide covers how to set up the necessary OpenType kerning lookup tables, open the Metrics window, and manually define individual kerning adjustments to achieve professional typographic results.

Step 1: Create a Kerning Lookup Table

FontForge manages kerning through OpenType GPOS (Glyph Positioning) tables. Before adding manual pairs, you must ensure a kerning lookup exists.

  1. Open your font project in FontForge.
  2. Navigate to Element > Font Info (or press Ctrl+Shift+F on Windows/Linux, Cmd+Shift+F on macOS).
  3. In the left sidebar, select Lookups, then click the GPOS tab at the top.
  4. Click Add Lookup.
  5. Set the Type dropdown to Pair Adjustment (Kerning).
  6. In the Feature column, select or type kern (Horizontal Kerning). Click OK.
  7. With the newly created lookup selected, click Add Subtable.
  8. Name the subtable or accept the default name, then click OK. When prompted for the subtable type, choose Individual kerning pairs (not kerning classes).

Step 2: Open the Metrics Window

While you can input kerning values numerically within the subtable settings, visual adjustment in the Metrics window is faster and more precise.

  1. In the main FontForge menu, go to Metrics > Open Metrics Window (or press Ctrl+K / Cmd+K).
  2. A text entry bar will appear at the top, along with a visual preview area below.
  3. In the text field, type the sequence of characters you want to kern (for example, AV, Wa, or LT).

Step 3: Manually Adjust the Kerning Value

  1. Click on the second character of the pair you want to adjust in the Metrics window.
  2. Look at the spacing line between the two glyphs.
  3. Adjust the kerning using one of the following methods:
    • Click and Drag: Click and hold the horizontal bar between the two characters in the preview window, then drag it left to decrease the space or right to increase it.
    • Manual Numeric Entry: In the metrics data table at the top of the window, locate the Kern field for that character pair and enter a positive or negative numeric value directly.
  4. The adjustment is instantly stored as an individual kerning pair under the GPOS subtable you created.

Step 4: Verify and Save

  1. Test other character pairings by typing full words into the text field (e.g., AVALANCHE, Towards).
  2. Once satisfied with the spacing, close the Metrics window.
  3. Save your project using File > Save (.sfd format).
  4. When exporting the final font via File > Generate Fonts, ensure the format supports OpenType features (such as OTF or TTF) so the GPOS kerning data is retained.