Web/API/TextMetrics

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.

Properties

TextMetrics.width Read only: Is a double giving the calculated width of a segment of inline text in CSS pixels. It takes into account the current font of the context.
TextMetrics.actualBoundingBoxLeft Read only: Is a double giving the distance 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. The distance is measured parallel to the baseline.
TextMetrics.actualBoundingBoxRight Read only: Is a double giving 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: Is a double giving 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: Is a double giving 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: Is a double giving 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: Is a double giving 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: Is a double giving 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: Is a double giving 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: Is a double giving 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: Is a double giving 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: Is a double giving 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

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

JavaScript

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(function (baseline, index) {
  let text = 'Abcdefghijklmnop (' + baseline + ')';
  let textMetrics = ctx.measureText(text);
  let y = 50 + index * 50;
  ctx.beginPath();
  ctx.fillText(text, 0, y);
  let lineY = y - Math.abs(textMetrics[baseline]);
  if (baselinesBelowAlphabetic.includes(baseline)) {
    lineY = y + Math.abs(textMetrics[baseline]);
  }
  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:

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(Math.abs(textMetrics.actualBoundingBoxLeft) +
            Math.abs(textMetrics.actualBoundingBoxRight));
// 462.8833333333333

Specifications

Specification
HTML Living StandardThe definition of 'TextMetrics' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`TextMetrics`	Chrome Full support 4	Edge Full support 12	Firefox Full support 1.5	IE Full support 9	Opera Full support 9	Safari Full support 3.1	WebView Android Full support Yes	Chrome Android Full support Yes	Firefox Android Full support 31	Opera Android Full support Yes	Safari iOS Full support Yes	Samsung Internet Android Full support Yes
`actualBoundingBoxAscent` Experimental'	Chrome Full support 77 Full support 77 No support ? — 77 Disabled' Disabled' Until version 77 (exclusive): this feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79	Firefox Full support 74	IE No support No	Opera ?	Safari Full support Yes	WebView Android Full support 77	Chrome Android Full support 77 Full support 77 No support ? — 77 Disabled' Disabled' Until version 77 (exclusive): this feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android Full support 12.0
`actualBoundingBoxDescent` Experimental'	Chrome Full support 77 Full support 77 No support ? — 77 Disabled' Disabled' Until version 77 (exclusive): this feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79	Firefox Full support 74	IE No support No	Opera ?	Safari Full support Yes	WebView Android Full support 77	Chrome Android Full support 77 Full support 77 No support ? — 77 Disabled' Disabled' Until version 77 (exclusive): this feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android Full support 12.0
`actualBoundingBoxLeft` Experimental'	Chrome Full support 77 Full support 77 No support ? — 77 Disabled' Disabled' Until version 77 (exclusive): this feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79	Firefox Full support 74	IE No support No	Opera ?	Safari Full support Yes	WebView Android Full support 77	Chrome Android Full support 77 Full support 77 No support ? — 77 Disabled' Disabled' Until version 77 (exclusive): this feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android Full support 12.0
`actualBoundingBoxRight` Experimental'	Chrome Full support 77 Full support 77 No support ? — 77 Disabled' Disabled' Until version 77 (exclusive): this feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79	Firefox Full support 74	IE No support No	Opera ?	Safari Full support Yes	WebView Android Full support 77	Chrome Android Full support 77 Full support 77 No support ? — 77 Disabled' Disabled' Until version 77 (exclusive): this feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android Full support 12.0
`alphabeticBaseline` Experimental'	Chrome Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79 Disabled' Full support 79 Disabled' Disabled' From version 79: this feature is behind the `Experimental Web Platform Features` preference.	Firefox Full support 74 Disabled' Full support 74 Disabled' Disabled' From version 74: this feature is behind the `dom.textMetrics.baselines.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera ?	Safari Full support Yes	WebView Android No support No	Chrome Android Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android No support No
`emHeightAscent` Experimental'	Chrome Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79 Disabled' Full support 79 Disabled' Disabled' From version 79: this feature is behind the `Experimental Web Platform Features` preference.	Firefox Full support 74 Disabled' Full support 74 Disabled' Disabled' From version 74: this feature is behind the `dom.textMetrics.emHeight.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera ?	Safari Full support Yes	WebView Android No support No	Chrome Android Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android No support No
`emHeightDescent` Experimental'	Chrome Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79 Disabled' Full support 79 Disabled' Disabled' From version 79: this feature is behind the `Experimental Web Platform Features` preference.	Firefox Full support 74 Disabled' Full support 74 Disabled' Disabled' From version 74: this feature is behind the `dom.textMetrics.emHeight.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera ?	Safari Full support Yes	WebView Android No support No	Chrome Android Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android No support No
`fontBoundingBoxAscent` Experimental'	Chrome Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79 Disabled' Full support 79 Disabled' Disabled' From version 79: this feature is behind the `Experimental Web Platform Features` preference.	Firefox Full support 74 Disabled' Full support 74 Disabled' Disabled' From version 74: this feature is behind the `dom.textMetrics.fontBoundingBox.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera ?	Safari Full support Yes	WebView Android No support No	Chrome Android Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android No support No
`fontBoundingBoxDescent` Experimental'	Chrome Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79 Disabled' Full support 79 Disabled' Disabled' From version 79: this feature is behind the `Experimental Web Platform Features` preference.	Firefox Full support 74 Disabled' Full support 74 Disabled' Disabled' From version 74: this feature is behind the `dom.textMetrics.fontBoundingBox.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera ?	Safari Full support Yes	WebView Android No support No	Chrome Android Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS No support No	Samsung Internet Android No support No
`hangingBaseline` Experimental'	Chrome Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79 Disabled' Full support 79 Disabled' Disabled' From version 79: this feature is behind the `Experimental Web Platform Features` preference.	Firefox Full support 74 Disabled' Full support 74 Disabled' Disabled' From version 74: this feature is behind the `dom.textMetrics.baselines.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera ?	Safari Full support Yes	WebView Android No support No	Chrome Android Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android No support No
`ideographicBaseline` Experimental'	Chrome Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Edge Full support 79 Disabled' Full support 79 Disabled' Disabled' From version 79: this feature is behind the `Experimental Web Platform Features` preference.	Firefox Full support 74 Disabled' Full support 74 Disabled' Disabled' From version 74: this feature is behind the `dom.textMetrics.baselines.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera ?	Safari Full support Yes	WebView Android No support No	Chrome Android Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `Experimental Web Platform Features` preference. To change preferences in Chrome, visit chrome://flags.	Firefox Android No support No	Opera Android ?	Safari iOS Full support Yes	Samsung Internet Android No support No
`width` Experimental'	Chrome Full support 4	Edge Full support 12	Firefox Full support 1.5	IE Full support 9	Opera Full support 9	Safari Full support 3.1	WebView Android Full support Yes	Chrome Android Full support Yes	Firefox Android Full support 31	Opera Android Full support Yes	Safari iOS Full support 3.2	Samsung Internet Android Full support Yes

Legend

Full support: Full support
No support: No support
Compatibility unknown: Compatibility unknown
Experimental. Expect behavior to change in the future.': Experimental. Expect behavior to change in the future.
User must explicitly enable this feature.': User must explicitly enable this feature.