TextMetrics

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

* Some parts of this feature may have varying levels of support.

Note: This feature is available in Web Workers.

The TextMetrics interface represents the dimensions of a piece of text in the canvas; a TextMetrics instance can be retrieved using the CanvasRenderingContext2D.measureText() method.

Instance properties

TextMetrics.width Read only

Returns the width of a segment of inline text in CSS pixels. It takes into account the current font of the context.

TextMetrics.actualBoundingBoxLeft Read only

Distance parallel to the baseline from the alignment point given by the CanvasRenderingContext2D.textAlign property to the left side of the bounding rectangle of the given text, in CSS pixels; positive numbers indicating a distance going left from the given alignment point.

TextMetrics.actualBoundingBoxRight Read only

Returns the distance from the alignment point given by the CanvasRenderingContext2D.textAlign property to the right side of the bounding rectangle of the given text, in CSS pixels. The distance is measured parallel to the baseline.

TextMetrics.fontBoundingBoxAscent Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the top of the highest bounding rectangle of all the fonts used to render the text, in CSS pixels.

TextMetrics.fontBoundingBoxDescent Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the bottom of the bounding rectangle of all the fonts used to render the text, in CSS pixels.

TextMetrics.actualBoundingBoxAscent Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the top of the bounding rectangle used to render the text, in CSS pixels.

TextMetrics.actualBoundingBoxDescent Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline attribute to the bottom of the bounding rectangle used to render the text, in CSS pixels.

TextMetrics.emHeightAscent Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the top of the em square in the line box, in CSS pixels.

TextMetrics.emHeightDescent Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the bottom of the em square in the line box, in CSS pixels.

TextMetrics.hangingBaseline Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the hanging baseline of the line box, in CSS pixels.

TextMetrics.alphabeticBaseline Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the alphabetic baseline of the line box, in CSS pixels.

TextMetrics.ideographicBaseline Read only

Returns the distance from the horizontal line indicated by the CanvasRenderingContext2D.textBaseline property to the ideographic baseline of the line box, in CSS pixels.

Examples

Baselines illustrated

This example demonstrates the baselines the TextMetrics object holds. The default baseline is the alphabeticBaseline. See also the CanvasRenderingContext2D.textBaseline property.

HTML

html
<canvas id="canvas" width="550" height="500"></canvas>

JavaScript

js
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");

const baselinesAboveAlphabetic = [
  "fontBoundingBoxAscent",
  "actualBoundingBoxAscent",
  "emHeightAscent",
  "hangingBaseline",
];
const baselinesBelowAlphabetic = [
  "ideographicBaseline",
  "emHeightDescent",
  "actualBoundingBoxDescent",
  "fontBoundingBoxDescent",
];
const baselines = [...baselinesAboveAlphabetic, ...baselinesBelowAlphabetic];
ctx.font = "25px serif";
ctx.strokeStyle = "red";

baselines.forEach((baseline, index) => {
  const text = `Abcdefghijklmnop (${baseline})`;
  const textMetrics = ctx.measureText(text);
  const y = 50 + index * 50;
  ctx.beginPath();
  ctx.fillText(text, 0, y);

  const baselineMetricValue = textMetrics[baseline];
  if (baselineMetricValue === undefined) {
    return;
  }

  const lineY = baselinesBelowAlphabetic.includes(baseline)
    ? y + Math.abs(baselineMetricValue)
    : y - Math.abs(baselineMetricValue);
  ctx.moveTo(0, lineY);
  ctx.lineTo(550, lineY);
  ctx.stroke();
});

Result

Measuring text width

When measuring the x-direction of a piece of text, the sum of actualBoundingBoxLeft and actualBoundingBoxRight can be wider than the width of the inline box (width), due to slanted/italic fonts where characters overhang their advance width.

It can therefore be useful to use the sum of actualBoundingBoxLeft and actualBoundingBoxRight as a more accurate way to get the absolute text width:

js
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
const text = "Abcdefghijklmnop";
ctx.font = "italic 50px serif";
const textMetrics = ctx.measureText(text);

console.log(textMetrics.width);
// 459.8833312988281

console.log(
  textMetrics.actualBoundingBoxRight + textMetrics.actualBoundingBoxLeft,
);
// 462.8833333333333

Specifications

Specification
HTML
# textmetrics

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
TextMetrics
actualBoundingBoxAscent
actualBoundingBoxDescent
actualBoundingBoxLeft
actualBoundingBoxRight
alphabeticBaseline
emHeightAscent
emHeightDescent
fontBoundingBoxAscent
fontBoundingBoxDescent
hangingBaseline
ideographicBaseline
width

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
No support
No support
User must explicitly enable this feature.

See also