TextMetrics

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

Instance properties

{{domxref("TextMetrics.width")}} {{ReadOnlyInline}}
- : Returns the width of a segment of inline text in CSS pixels. It takes into account the current font of the context.
{{domxref("TextMetrics.actualBoundingBoxLeft")}} {{ReadOnlyInline}}
- : Distance parallel to the baseline from the alignment point given by the {{domxref("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.
{{domxref("TextMetrics.actualBoundingBoxRight")}} {{ReadOnlyInline}}
- : Returns the distance from the alignment point given by the {{domxref("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.
{{domxref("TextMetrics.fontBoundingBoxAscent")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("CanvasRenderingContext2D.textBaseline")}} attribute to the top of the highest bounding rectangle of all the fonts used to render the text, in CSS pixels.
{{domxref("TextMetrics.fontBoundingBoxDescent")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("CanvasRenderingContext2D.textBaseline")}} attribute to the bottom of the bounding rectangle of all the fonts used to render the text, in CSS pixels.
{{domxref("TextMetrics.actualBoundingBoxAscent")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("CanvasRenderingContext2D.textBaseline")}} attribute to the top of the bounding rectangle used to render the text, in CSS pixels.
{{domxref("TextMetrics.actualBoundingBoxDescent")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("CanvasRenderingContext2D.textBaseline")}} attribute to the bottom of the bounding rectangle used to render the text, in CSS pixels.
{{domxref("TextMetrics.emHeightAscent")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("CanvasRenderingContext2D.textBaseline")}} property to the top of the em square in the line box, in CSS pixels.
{{domxref("TextMetrics.emHeightDescent")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("CanvasRenderingContext2D.textBaseline")}} property to the bottom of the em square in the line box, in CSS pixels.
{{domxref("TextMetrics.hangingBaseline")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("CanvasRenderingContext2D.textBaseline")}} property to the hanging baseline of the line box, in CSS pixels.
{{domxref("TextMetrics.alphabeticBaseline")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("CanvasRenderingContext2D.textBaseline")}} property to the {{glossary("/Baseline/Typography", "alphabetic baseline")}} of the line box, in CSS pixels.
{{domxref("TextMetrics.ideographicBaseline")}} {{ReadOnlyInline}}
- : Returns the distance from the horizontal line indicated by the {{domxref("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 {{domxref("CanvasRenderingContext2D.textBaseline")}} property.

HTML

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((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:

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