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2.0.0 • Public • Published



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.

$ npm i --save capsize
import capsize from 'capsize';

const styles = capsize({
  capHeight: 16,
  lineGap: 8,
  fontMetrics: {
    capHeight: 700,
    ascent: 1058,
    descent: -291,
    lineGap: 0,
    unitsPerEm: 1000,


Text size

Capsize supports two methods of defining the size of text, capHeight and fontSize.

NOTE: You should only ever pass one or the other, not both.

capHeight: <number>

Sets the height of the capital letters to the defined value. Defining typography in this way makes aligning to a grid or with other elements, e.g. icons, a breeze.

Highlighting the cap height

fontSize: <number>

Setting the font size allows you to get all the benefits of the white space trimming, while still specifying an explicit font-size for your text. This can be useful when needed to match a concrete design spec or fitting into an existing product.

Highlighting the font size

Line height

Capsize supports two mental models for specifying line height, lineGap and leading. If you pass neither the text will follow the default spacing of the specified font, e.g. line-height: normal.

NOTE: You should only ever pass one or the other, not both.

lineGap: <number>

Sets the number of pixels between lines, as measured between the baseline and cap height of the next line.

Highlighting the line gap

leading: <number>

Sets the line height to the provided value as measured from the baseline of the text. This aligns the web with how typography is treated in design tools.

Highlighting the leading

Font Metrics

This metadata is extracted from the metrics tables inside the font itself. You can use the Capsize website to find these by selecting a font and referencing JavaScript tab in step 3.



Returns the actual rendered cap height for a specific font size given the provided font metrics.

import { getCapHeight } from 'capsize';

const actualCapHeight = getCapHeight({
  fontSize: 24,
  fontMetrics: {



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