How to implement max-font-size?

Question

I want to specify my font size using vw, as in

font-size: 3vw;

However, I also want to limit the font size to say 36px. How can I achieve the equivalent of max-font-size, which does not exist--is the only option to use media queries?

Answer 1

font-size: 3vw; means that the font size will be 3% of the viewport width. So when the viewport width is 1200px - the font size will be 3% * 1200px = 36px.

So a max-font-size of 36px can be easily implemented using a single media query to override the default 3vw font-size value.

Codepen demo (Resize Browser)

div {
  font-size: 3vw;
}
@media screen and (min-width: 1200px) {
  div {
     font-size: 36px;
  }
}

<div>hello</div>

---

Update: With the new CSS min() function, we can simplify the above code - without using media queries (caniuse)

div {
  font-size: min(3vw, 36px);
}

In the above example, the font-size will be at most 36px, but will decrease to 3vw if the the viewport is less than 1200px wide (where 3vw computes to a value less than 36px )

---

That being said, using viewport units for font-size in the above way is problematic because when the viewport width is much smaller - say 320px - then the rendered font size will become 0.03 x 320 = 9.6px which is very (too) small.

In order to overcome this problem, I can recommend using a technique called Fluid Type AKA CSS Locks.

A CSS lock is a specific kind of CSS value calculation where:

• there is a minimum value and a maximum value,
• and two breakpoints (usually based on the viewport width),
• and between those breakpoints, the actual value goes linearly from the minimum to the maximum.

So let's say we want to apply the above technique such that the minimum font-size is 16px at a viewport width of 600px or less, and will increase linearly until it reaches a maximum of 32px at a viewport width of 1200px.

This can be represented as follows (see this CSS-tricks article for more details):

div {
  font-size: 16px;
}
@media screen and (min-width: 600px) {
  div {
    font-size: calc(16px + 16 * ((100vw - 600px) / 600));
  }
}
@media screen and (min-width: 1200px) {
  div {
    font-size: 32px;
  }
}

Alternatively, we could use this SASS mixin which does all of the math for us so that the CSS would look something like this:

/* 
     1) Set a min-font-size of 16px when viewport width < 600px
     2) Set a max-font-size of 32px when viewport width > 1200px and
     3) linearly increase the font-size from 16->32px 
     between a viewport width of 600px-> 1200px 
*/

div {
  @include fluid-type(font-size, 600px, 1200px, 16px, 32px);
}

// ----
// libsass (v3.3.6)
// ----

// =========================================================================
//
//  PRECISE CONTROL OVER RESPONSIVE TYPOGRAPHY FOR SASS
//  ---------------------------------------------------
//  Indrek Paas @indrekpaas
//
//  Inspired by Mike Riethmuller's Precise control over responsive typography
//                                                                         
//
//  `strip-unit()` function by Hugo Giraudel
//  
//  11.08.2016 Remove redundant `&` self-reference
//  31.03.2016 Remove redundant parenthesis from output
//  02.10.2015 Add support for multiple properties
//  24.04.2015 Initial release
//
// =========================================================================

@function strip-unit($value) {
  @return $value / ($value * 0 + 1);
}

@mixin fluid-type($properties, $min-vw, $max-vw, $min-value, $max-value) {
  @each $property in $properties {
    #{$property}: $min-value;
  }

  @media screen and (min-width: $min-vw) {
    @each $property in $properties {
      #{$property}: calc(#{$min-value} + #{strip-unit($max-value - $min-value)} * (100vw - #{$min-vw}) / #{strip-unit($max-vw - $min-vw)});
    }
  }

  @media screen and (min-width: $max-vw) {
    @each $property in $properties {
      #{$property}: $max-value;
    }
  }
}

// Usage:
// ======

// /* Single property */
// html {
//   @include fluid-type(font-size, 320px, 1366px, 14px, 18px);
// }

// /* Multiple properties with same values */
// h1 {
//   @include fluid-type(padding-bottom padding-top, 20em, 70em, 2em, 4em);
// }

////////////////////////////////////////////////////////////////////////////

div {
  @include fluid-type(font-size, 600px, 1200px, 16px, 32px);
}
@media screen and (max-width: 600px) {
  div {
     font-size: 16px;
  }
}
@media screen and (min-width: 1200px) {
  div {
     font-size: 36px;
  }
}

<div>Responsive Typography technique known as Fluid Type or CSS Locks. 
  Resize the browser window to see the effect.
</div>

Codepen Demo

---

Update: We can use the new clamp() CSS function (caniuse) to refactor the above code to simply:

div {
  font-size: clamp(16px, 3vw, 32px);
}

see MDN:

clamp() allows you to set a font-size that grows with the size of the viewport, but doesn't go below a minimum font-size or above a maximum font-size. It has the same effect as the code in Fluid Typography but in one line, and without the use of media queries.

p { font-size: clamp(1rem, 2.5vw, 1.5rem); }
<p>
If 2.5vw is less than 1rem, the font-size will be 1rem.
If 2.5vw is greater than 1.5rem, the font-size will be 1.5rem.
Otherwise, it will be 2.5vw.
</p>

--

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Further Reading

Fluid Typography

How Do You Do max-font-size in CSS?

Fluid Responsive Typography With CSS Poly Fluid Sizing

Non-linear interpolation in CSS