The Kern Center is a sheet for editing the font’s kerning. It can be opened by clicking on the Kerning icon in the font’s toolbar.

Power users are advised to use Metrics Machine, a more powerful kerning tool than Kern Center. Metrics Machine is available as an extension for RoboFont 3 / UFO3, and as a separate app for RoboFont 1 / UFO2.

In RoboFont 1.8, if Metrics Machine is installed, clicking the Kerning icon will send the font to Metrics Machine for editing. Use ⌥ + click to open the Kern Center instead.

At the top of the Kern Center is a table with all kerning pairs in the font, one per row. The first two columns show the 1st and 2nd glyphs (or glyph groups) in the kerning pair, the third column shows the kerning value. Below the table are an input field and a preview of all glyph combinations defined by the selected pair.

Some notes about kerning

Use groups to represent large amounts of kerning data with relatively few pairs.

  • Members of kerning pairs can be glyph names or group names.
  • In UFO3, kerning group names must use a standard prefix: public.kern1. (1st glyph in kerning pair) or public.kern2. (2nd glyph in pair).
  • Kerning pairs are writing direction neutral. If text is written left-to-right, the first glyph is the left-most glyph; if text is written right-to-left, the first glyph is the right-most one.

Read more about kerning in the UFO3 documentation.

Add a note about kerning differences between RF1/UFO2 and RF3/UFO3.


Kerning table

action description
select a kerning pair Update the input field and the kerning preview.
enter Edit the kerning value.

Kern preview

action description
click Select a kerning pair.
click + drag (preview) Modify the kerning value interactively by moving the glyphs.
arrow keys (left or right) Subtract or add 1 unit to the kerning value.
⇧ + arrow left or right Subtract or add 10 units to the kerning value.
⇧ + ⌘ + arrow keys Subtract or add 100 units to the kerning value.
tab Select next kerning pair.
⇧ + tab Select previous kerning pair.

Control Buttons

action description
+ Add kerning pair.
- Remove kerning pair.
Kerning Apply kerning to the font.
Left To Right Toggle between left-to-right and right-to-left.
Prefer Group Kerning If a kerning group is found for the edited glyph, it is used. Otherwise, the glyph is used.

How-To: Adding kern pairs to a font

Last edited on 23/01/2018