Flipping how we define
typography in CSS

Capsize makes the sizing and layout of text as predictable as every other element on the screen.

Using font metadata, text can now be sized according to the height of its capital letters while trimming the space above capital letters and below the baseline.

1. Choose a font

    Em square (2048)

    Cap Height (1456)

    Descender (500)

    Ascender (1900)

    Line Height


    2. Adjust size & spacing

    Lorem ipsum Lolor sit amet, Lonsectetur adipiscing elit. Duis eu ornare nisi, sed feugiat metus. Pellentesque rutrum vel metus non dignissim. Aenean egestas neque mattis mi maximus luctus. Praesent et commodo dui, nec eleifend lectus. Pellentesque blandit nisi tellus, id efficitur urna consectetur id. Sed convallis tempor dui vel aliquet.

    3. Apply the styles

    import capsize from 'capsize';
    const fontMetrics = {
      capHeight: 1456,
      ascent: 1900,
      descent: -500,
      lineGap: 0,
      unitsPerEm: 2048
    const styles = capsize({
      capHeight: 48,
      lineGap: 24


    Why use pseudo elements instead of applying the negative margin directly?

    The negative margins are applied to pseudo elements to guard against margin collapse. Combining the use of pseudo elements and padding on the parent container prevents the margins from being collapsed into the parent element. The collapsing is most visible when text is used directly inside a container that has a background colour applied.

    What is the recommended way to handle metrics for fallback fonts?

    Until the trimming of leading and trailing white space around text is natively supported in CSS, supporting fallback fonts perfectly will have its trade-offs.

    Typically the font stack should not specify wildly different font families as fallbacks, and in practice that means the cap heights and descenders should have similar scales proportionate to their font. While not having a pixel-perfect match to the font, it should still perform the trim effectively enough.

    For web fonts that are more display focused, using a library such as webfontloader would allow applying fallback metrics as a separate class.

    What is the recommended way to handle text overflow/truncation?

    Applying standard text overflow techniques on the same element will result in descenders/ascenders getting cut off due to the overflow needing to be hidden, e.g.:.truncate {
      text-oveflow: ellipsis;
      overflow: hidden;
      white-space: nowrap;
    Ideally you should not be adding further layout-related styles to the element that is capsized to prevent styles possibly clashing with the trim. We handle this by applying the truncation styles to a block level span element, e.g.:<p class="capsizedText">
      <span class="truncate">
    If using a component system you can conditionally add the span only when using truncation.

    What does this mean for diacritic and accent marks in non-Latin alphabets?

    Diacritics and accent marks can have an impact on the perceived cap height and baseline. Given the location of the marks being at the extremities of the fonts line box, it is necessary to increase the white space by increasing the line-height and container padding to accomodate. This is the case today even without using Capsize.

    What can browser vendors do to make this easier?

    Going forward, it would be great if this power was built into the platform and able to be applied through standard CSS properties. The CSS Working Group have a number proposals/specifications that would simplify this significantly.

    Relevant specifications include:

    These specifications would turn the CSS generated by Capsize into:.capsizedText {
      font-size: 48cap;
      line-height: 72px;
      leading-trim: cap ideographic;

    Currently, there is no proposal for a way to define the line-height using the lineGap style mental model. With the rise of properties like gap for CSS grid (and soon flexbox?) maybe this will feed into a future proposal.