---
title: Millimeter options
---
:::warning
While FreeSewing supports millimeter options, we recommend
using [percentage options][1]. While there are [good
reasons](#when) to use millimeter options, we may reject
contributions that (ab)use them outside of a valid use case.
:::
## Structure
A millimeter option should be a plain object with these properties:
- `mm` : The default value in millimeters
- `min` : The minimum that's allowed
- `max` : The maximum that's allowed
## Example
```js
options: {
elasticWidth: {
mm: 35,
min: 5,
max: 80
}
}
```
:::note COMMENT (by joost)
#### What's wrong with millimeter options?
Millimeter options do not scale.
Parametric design is the _raison d'être_ of FreeSewing and that core belief
that things should seamlessly adapt goes out the window when you use a `mm`
option because now you have a value that will not change based on the
input measurements.
When you need a millimeter option, reach for a [snapped
percentage option][1] instead.
#### When to use millimeter options?
There are some use-cases where a millimeter option makes sense.
This is not an exhaustive list, so use your own judgement.
###### When the option is a de-facto measurement {#when}
When an option functions as a de-facto measurement, you should use a millimeter
option. For example, when you are designing a tent pattern, the length of the
tent makes perfect sense as a millimeter option as FreeSewing does not have a
_length-of-tent_ measurements, and adding one does not make a lot of sense.
:::
[1]: /reference/api/part/config/options/pct
