Clamped Values

CSS has scalable units like %, the viewport-percentage lengths (vw, vh, vmin, and vmax) and even more. Another type of scalable unit not part of CSS that some designers with with is the idea of the element-based unit. With all of these, there might be the desire to ‘clamp’ the value with a certain minimum or maximum value, effectively setting a range for the scalable value that it cannot exceed.

Thankfully CSS has a minmax() function that acts like a number clamp in some situations, but unfortunately it’s limited to the Grid display module. There are a number of situations when styling websites where being able to clamp scalable units would be helpful, including sizing fonts, setting percentage-based margins and padding, and much more. It’s unfortunate that CSS’s minmax() function is too limited to work in these cases, but there are workarounds. In the future CSS is gaining min() and max() functions which will be able to be used anywhere, and even nested within each other to perform number clamping like min(max(10px, 10vw, 100px)).

Parts Required

JS Tests

In order to clamp a scalable value using JavaScript you need a small amount of logic. I’ve expressed the logic three different ways below, but the most efficient expression is:

Math.min(Math.max(min, mid), max)

Number clamp utility function using if:

function ifClamp(min, mid, max) {

  if (min < mid && mid < max) {

    return mid

  } else if (mid < min) {

    return min

  } else if (max < mid) {

    return max



Number clamp utility function using ternary expressions:

function ternaryClamp(min, mid, max) {

  return mid < min ? min : mid < max ? mid : max


Number clamp utility function using Math.min() and Math.max():

function mathClamp(min, mid, max) {

  return Math.min(Math.max(min, mid), max)


Plugins Capable

Syntax Examples


@element .demo {
  $this {
    font-size: eval("Math.min(Math.max(10, offsetWidth/10), 100)")px;

Scoped Eval Mixin

scoped('.demo', `
  font-size: eval(Math.min(Math.max(10, this.offsetWidth/10), 100))px;


Further Reading