“Extrusion Depth” (`EDPT` in CSS) is an [axis](/glossary/axis_in_variable_fonts) found in some [variable fonts](/glossary/variable_fonts) that can be used to control the depth of three-dimensional letterforms. Values are in thousandths of an [em](/glossary/em) (the current font size). For example, setting Extrusion Depth to 500 will result in a 50%-of-the-em extrusion, which would be 20 px if the font size is set to 40 px.

The [Google Fonts CSS v2 API](https://developers.google.com/fonts/docs/css2) defines the axis as:

| Default: | Min: | Max: | Step: |
| --- | --- | --- | --- |
| 100 | 0 | 1000 | 1 

Note that the default value is expected to differ per family, rather than be universally set for any implementation of this axis.

<figure>

![An image showing two type specimens, each with an axis slider underneath. The specimen on the left shows the effects of the axis’ lowest value. The specimen on the right shows the effects of the axis’ highest value.](images/thumbnail.svg)

</figure>

<figcaption>Note the two-dimensional appearance when the axis is set to 0 when using the <a href="https://fonts.google.com/specimen/Nabla">Nabla</a> font.</figcaption>

The axis was first used in the [Nabla font](https://fonts.google.com/specimen/Nabla) [color font](/glossary/color_fonts), which uses isometric perspective to achieve its three-dimensional look. The extrusion depth, at its maximum setting, creates a deeper or thicker letterform. At its minimum setting, the letterform appears only two-dimensional.