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In jsPDF, image size is controlled in the PDF document’s units—not automatically in CSS pixels. For a direct image, pass x, y, width, and height to addImage(). For HTML conversion with doc.html(), set the target width and position in jsPDF units, and coordinate those values with html2canvas’s scale and windowWidth options.
The reliable workflow is: choose the page format and unit system, calculate the available content box, preserve the source aspect ratio, then check pagination and cross-origin loading.
Understand the two size systems
HTML-to-PDF workflows involve at least two coordinate systems:
- PDF placement units: millimeters, points, inches, or another unit selected when creating the jsPDF instance.
addImage()uses these units for position and size. - Canvas pixels: html2canvas renders HTML into a pixel-based canvas. Its pixel width and height are not automatically equivalent to millimeters, points, or inches in the PDF.
Confusing these systems is the main reason an image appears unexpectedly large, tiny, stretched, or clipped.
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Choose the page and unit system first
Create the document with the paper format, orientation, and units you intend to use. jsPDF defaults to A4 portrait with millimeter units, but you can select another orientation, unit, or custom page format.
import { jsPDF } from "jspdf";
const doc = new jsPDF({
orientation: "portrait",
unit: "mm",
format: "a4"
});
Every later image measurement must use the same unit. If the document uses pt, a width of 200 means 200 points; it does not mean 200 CSS pixels.
Set an image size with addImage()
The direct API is doc.addImage(imageData, format, x, y, width, height, ...). The API accepts data URLs and image, canvas, or buffer forms. x and y measure from the page’s left and top edges; width and height are in the configured PDF units.
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doc.addImage(
imageData,
"PNG",
20, // x in mm
30, // y in mm
170, // width in mm
95 // height in mm
);
doc.save("image.pdf");
The method description in the jsPDF API is straightforward: it “Adds an Image to the PDF.” Because the API receives both dimensions, it will use exactly the rectangle you provide. It does not infer a proportional height for you.
Preserve the image’s aspect ratio
To avoid distortion, derive one dimension from the other and the image’s intrinsic dimensions:
targetHeight = intrinsicHeight × targetWidth ÷ intrinsicWidth
getImageProperties() can provide the intrinsic width and height for image data. The following pattern fits an image between left and right margins while retaining its proportions.
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const leftMargin = 20;
const rightMargin = 20;
const top = 30;
const pageWidth = doc.internal.pageSize.getWidth();
const targetWidth = pageWidth - leftMargin - rightMargin;
const props = doc.getImageProperties(imageData);
const targetHeight = (props.height * targetWidth) / props.width;
doc.addImage(
imageData,
"PNG",
leftMargin,
top,
targetWidth,
targetHeight
);
This is an aspect-ratio calculation, not a special automatic sizing mode. If you instead know the desired height, calculate targetWidth = intrinsicWidth × targetHeight ÷ intrinsicHeight.
Keep the result inside the page
Fitting the width does not guarantee that the image fits vertically. Calculate the usable height from the page height and your top and bottom margins:
const pageHeight = doc.internal.pageSize.getHeight();
const bottomMargin = 20;
const availableHeight = pageHeight - top - bottomMargin;
let width = targetWidth;
let height = targetHeight;
if (height > availableHeight) {
height = availableHeight;
width = (props.width * height) / props.height;
}
doc.addImage(imageData, "PNG", leftMargin, top, width, height);
If the image is taller than one page even after scaling, choose a policy explicitly: scale it to one page, crop it, or split it across pages. A single addImage() call does not make one oversized image flow naturally through multiple pages.
Size HTML rendered with doc.html()
When the source is a DOM element, doc.html(element, options) renders the element through html2canvas and places the result in the PDF. Its documented x, y, and target width are jsPDF units.
const element = document.querySelector("#invoice");
const doc = new jsPDF({
unit: "mm",
format: "a4",
orientation: "portrait"
});
doc.html(element, {
x: 15,
y: 15,
width: 180,
autoPaging: "text",
html2canvas: {
useCORS: true,
windowWidth: element.scrollWidth
},
callback: (pdf) => pdf.save("invoice.pdf")
});
The width option is connected to html2canvas configuration. jsPDF’s documentation warns that the target width has no effect when html2canvas.scale is specified or when windowWidth is not specified. Treat these as one layout configuration: set the viewport you want html2canvas to reproduce, set a PDF target width, and verify the output with the jsPDF version installed in your project.
Do not equate CSS pixels with PDF units
Your element may be 1200 pixels wide in the browser while the PDF target is 180 mm. html2canvas’s canvas dimensions remain pixels; the final placement width remains millimeters (or whichever unit you chose). Changing scale changes rasterization density, not the meaning of the PDF’s placement units.
Control image quality and file size
Rendering scale and image encoding affect sharpness and output size independently of placement dimensions. A larger html2canvas scale can create a denser raster image, but it can also increase memory use and PDF size. JPEG, PNG, and WebP have different size and transparency characteristics; a wrapper such as html2pdf.js exposes encoding and quality controls, but those controls belong to that wrapper and should not be treated as guarantees for every direct doc.html() configuration.
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Use PNG when lossless detail or transparency matters. Consider JPEG for photographic content when transparency is unnecessary. Choose a scale high enough for the intended viewing or printing size, then test memory use on your largest page.
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| Approach | Best for | Size control | Trade-offs |
|---|---|---|---|
doc.html() |
Capturing a DOM element’s layout | Target width, x, and y in jsPDF units, coordinated with html2canvas options |
Rendering depends on browser layout, cross-origin access, canvas limits, and the installed version |
addImage() |
Placing a known image precisely | Explicit x, y, width, and height |
You must calculate aspect ratio and pagination yourself |
| html2pdf.js wrapper | Convenient page-break controls around HTML capture | Wrapper options for page breaks, image type, and quality | It rasterizes rendered content and documents canvas and output-size limitations |
Make cross-origin images render
An image can have correct dimensions and still be blank. Browser security rules may prevent html2canvas from reading pixels hosted on another origin. The html2canvas options include useCORS and proxy, but success depends on the source server’s headers and your browser environment.
- Serve images with appropriate cross-origin permissions.
- Try
useCORS: truewhen the image server permits it. - Use a proxy only when you control or trust that proxy and understand its caching and security behavior.
- Wait until images have loaded before calling
doc.html().
Troubleshooting common sizing failures
The image is much too large or too small
Check the document’s unit and the values passed to addImage(). A canvas width in pixels is not automatically a width in millimeters, points, or inches. Convert or calculate dimensions in the document’s configured units.
html() ignores my width
Review whether you explicitly set html2canvas.scale and whether windowWidth is present. The jsPDF documentation ties target-width behavior to these options. Remove an unnecessary scale override, provide the intended window width, and retest with your installed version.
The image is stretched
You supplied width and height that do not share the source aspect ratio. Read intrinsic dimensions with getImageProperties() and derive the second dimension rather than hard-coding unrelated values.
The image is clipped or runs off the page
Compare the final rectangle with doc.internal.pageSize.getWidth() and getHeight(), subtracting all margins. For HTML, inspect the rendered element’s width and the selected autoPaging behavior. Decide whether to scale, crop, or paginate; do not assume an oversized image will flow automatically.
The PDF is blank or an image is missing
Check that the source data is valid, that the image has finished loading, and that cross-origin access is allowed. For HTML conversion, confirm html2canvas is available as the optional rendering dependency and inspect browser console errors.
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The output is blurry or unexpectedly large
Adjust rendering scale and encoding separately from placement width. Higher scale can improve detail while increasing memory and file size. Choose PNG, JPEG, or WebP according to transparency and photographic-detail needs, and test the largest document your users will generate.
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Frequently Asked Questions
Can jsPDF automatically keep an image’s proportions?
No. Because addImage() accepts both width and height, calculate one dimension from the other using the source image’s intrinsic aspect ratio.
Should I size an image in pixels or millimeters?
Use the PDF document’s configured units for addImage() and html() placement. Pixels describe the html2canvas raster and are a separate concern.
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Why does html2canvas scale change sharpness but not my PDF width?
Scale changes the rasterization density of the canvas. The PDF placement width is still controlled by the jsPDF target width and unit system.
When should I use a wrapper such as html2pdf.js?
Use it when its page-break and encoding conveniences outweigh rasterization, selectable-text, canvas-size, and output-file trade-offs for your document.
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