There has been a lot of discussion about what units of measure should be used for which areas of a website. When do we use PX, when do we use EM or REM or other units?

There are a lot of blogs out there including this one over at Engage Interactive which can shed some light on this, and whether they’re right or wrong is not for me to decide.

The issue that I wanted to solve is the actual development workflow. We default to literals. It’s hard to understand how large a rem or em value is, especially if it’s not a whole number. Assuming a base context of16px,8px makes more sense than writing 0.5rem. On top of that, we have to remember what requires rem, em, unitless, etc. and that’s just not how my brain works most of the time.

Enter postcss-unit-conversion. A simple PostCSS plugin to provide the ability to automatically convert all of the various unit values to EM or REM and allow you to write everything in pixels.

These defaults can be overwritten by simply set a few variables defining your base context, how many decimal places you’d like your value, and which units should be EM and which should be REM. Pixel values will remain pixels.

var options = {
    base: 16,
    precision: 3,
    toEM: [
    toREM: [

Easy as pie. I’d like to extend this, later on, ignore certain selectors or elements if necessary and keep it up to date with the latest WebPack and PostCSS versions.

Happy coding!