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keep font-size in proportion with its containers size


npm install flowtype

then in your app:

var flowtype = require('flowtype')


flowtype(el, [options])

setup flowtype on el taking an optional options object. Possible settings are:

  • min: desired font size in pixels when at el's min-width
  • max: desired font size in pixels when at el's max-width
  • minWidth: overrides el's real min-width
  • maxWidth: overrides el's real max-width
  • lineRatio: size of line-height relative to the font-size. defaults to 1.45
flowtype(document.body, {
  maxWidth: '800px', // can be a CSS value or a Number 
  minWidth: '300px',
  lineRatio: 1.45,
  min: 14,
  max: 22

In the above example when the document is 800px or wider flowtype will set the font size to 22px. When the document is 300px or less it will be set the font size to 14px. And when the document is at any width between 300px and 800px it will set the font size to match proportionally. e.g. if the document was 500px wide thats 40% of the distance from 300px to 800px so the font size will be set to 40% of the distance from 14px to 22px which is 17.2px.

Note: flowtype sets font size in pixels on the el you passed in. So you need to ensure that any children inside el have their font set in ems. Unless you want their font size to stay fixed.

Running the example

Just run make and navigate your browser to it.


This is based on flowtype.js by simple focus.