Default Glyph Grid Size in FontForge

This guide explains the default glyph grid size in the FontForge font editor, detailing the standard Em unit measurements, ascent and descent splits, and how to adjust these settings for different font formats.

The Default Grid: 1000 Units per Em

When you create a new font in FontForge, the default glyph canvas or grid size is set to an Em size of 1000 units (also known as Units per Em, or UPM).

This 1000-unit Em square is partitioned into two primary vertical metrics:

• Ascent: 800 units (the space above the baseline)
• Descent: 200 units (the space below the baseline)

In addition to the Em boundary, FontForge snaps coordinate points to an integer grid where the default snap resolution is 1 unit.

Why FontForge Uses 1000 Units

The 1000 UPM standard originates from Adobe PostScript Type 1 and OpenType-CFF (.otf) font specifications. A base-10 value of 1000 simplifies decimal scaling and layout calculations.

By contrast, TrueType fonts (.ttf) traditionally use power-of-two sizes, typically 2048 units (or occasionally 1024 units), to maximize rendering efficiency in TrueType rasterizers.

How to Change the Grid Size in FontForge

If you are developing a TrueType font or need a custom grid scale, you can change the default dimensions at any time:

1. Open your project in FontForge.
2. Go to the top menu and select Element > Font Info.
3. In the sidebar of the Font Info dialog, click General.
4. Locate the Em Size field. Enter your desired value (such as 2048).
5. Adjust the Ascent and Descent values accordingly (for a 2048 grid, a common split is 1638 ascent and 410 descent).
6. Click OK to apply the changes. FontForge will offer to automatically rescale your existing glyph outlines to fit the new grid dimensions.