To make a Puppeteer PDF match an emulated device viewport, configure the viewport and PDF page independently. Set the viewport in CSS pixels, choose the CSS media type you want rendered, and then set the PDF paper dimensions and fit behavior. deviceScaleFactor is not the PDF page-size control: page.pdf() has its own scale option.
Why the emulated viewport does not set the PDF size
Puppeteer controls two different stages of rendering. The viewport determines the browser’s emulated layout area; its width and height are CSS pixels. The viewport also has a separate deviceScaleFactor property. PDF generation, by contrast, uses print-to-PDF settings such as paper dimensions and PDF scale.
As a result, setting a phone-sized viewport does not, by itself, produce a PDF whose page is phone-sized. Nor does increasing the emulated device pixel ratio directly enlarge the PDF page. To get the intended result, decide what layout should be captured, what dimensions each PDF page should have, and whether the content should be scaled to fit those dimensions.
Choose the CSS media type first
page.pdf() generates a PDF using the print CSS media type by default. A site may have different styles for print and screen: navigation may disappear, text sizes may change, or a layout may reflow. If the PDF should use the page’s screen styles, call await page.emulateMediaType('screen') before page.pdf(). This changes the active media type; it does not set the PDF page dimensions.
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If print styling is the desired output, leave the default media type in place and check the site’s print-specific CSS. Do not try to correct a print-versus-screen layout difference solely by changing the PDF scale.
Set the emulated device before navigation
Set the viewport or emulate a device before loading the target page. Puppeteer’s Page.emulate(device) method is a shortcut that sets the user agent and viewport and resizes the page. Puppeteer advises emulating before navigation because some sites do not expect a phone or other device profile to be applied after they have loaded.
For a custom viewport, Page.setViewport() lets you set values such as CSS-pixel width and height, device scale factor, and mobile emulation. For a named device profile, use Page.emulate(device) with a device descriptor available in the Puppeteer version you are running. Either way, confirm that the site is actually laying out at the intended viewport: the page’s own responsive behavior, including its viewport metadata, affects what you see.
Set the PDF page size and fit behavior
Choose the PDF dimensions with format, width, or height in page.pdf(), or define a page size in CSS with @page. If format is set, it takes priority over width and height; avoid specifying conflicting values and expecting the explicit width and height to win.
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When the CSS @page size should control the PDF, set preferCSSPageSize: true. Its documented default is false; in that default mode, content is scaled to fit the paper size provided through the PDF options. The separate PDF scale option has a documented range of 0.1 to 2 and a default of 1. It controls PDF rendering scale, not viewport device pixel ratio.
For a viewport-shaped PDF, decide what physical or CSS-unit page dimensions make sense for the intended output, then use matching dimensions and verify the generated PDF. A viewport of 390 by 844 CSS pixels does not establish a universally correct PDF size or scale value. The right result depends on the page, media styles, chosen units, paper dimensions, and Chromium/Puppeteer version.
Runnable example: emulate a mobile viewport and create a PDF
The following Node.js example uses Puppeteer, a custom 390-by-844 CSS-pixel viewport, screen media, and explicit CSS-pixel PDF dimensions. It illustrates the separation between layout viewport and PDF page settings; it is not a universal device-to-paper conversion formula. Install Puppeteer in your project before running it, and change the URL and output path as needed.
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
try {
const page = await browser.newPage();
await page.setViewport({
width: 390,
height: 844,
deviceScaleFactor: 3,
isMobile: true,
});
await page.goto('https://example.com', {
waitUntil: 'networkidle0',
});
// Use screen CSS rather than page.pdf()'s print CSS default.
await page.emulateMediaType('screen');
await page.pdf({
path: 'viewport.pdf',
width: '390px',
height: '844px',
preferCSSPageSize: true,
scale: 1,
});
} finally {
await browser.close();
}
})();Here, deviceScaleFactor: 3 is a viewport property, while scale: 1 is a PDF option. The example intentionally sets them independently. If you want print styling, omit the emulateMediaType('screen') call. If the document’s CSS @page dimensions should determine the output page, keep preferCSSPageSize: true and define an appropriate @page size in the site’s CSS instead of assuming the example dimensions fit every document.
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Validate the output instead of guessing a scale formula
Puppeteer’s options identify the controls, but they do not establish one numeric scale formula that works for every website, stylesheet, paper size, and browser build. Inspect PDFs from representative pages and target device profiles. Check the page dimensions, whether content is clipped or unexpectedly small, and whether the rendered layout is the intended screen or print version.
- Confirm the page loaded at the intended viewport before generating the PDF.
- Check whether print CSS or screen CSS is active.
- Confirm which setting controls the page size: PDF dimensions or CSS
@page. - Check whether content is being fitted to paper or rendered using a CSS page size that takes priority.
- Change PDF
scaleonly after those other choices are correct, then inspect the resulting file.
Troubleshooting common sizing problems
The PDF is paper-sized instead of phone-sized
A mobile viewport does not automatically define the PDF page size. Set the intended dimensions using PDF options, or define a CSS @page size and enable preferCSSPageSize: true. Check whether format is set: when it is, it takes priority over PDF width and height.
The PDF layout does not look like the browser window
This is often a media-type mismatch. PDF generation uses print CSS by default. Call page.emulateMediaType('screen') before page.pdf() if the screen stylesheet is what you want. If the print layout is intended, inspect the site’s print styles rather than forcing screen media.
The output looks too small or too large
First check page dimensions, CSS page-size priority, and whether content is being fitted to paper. Then check PDF scale, which is independent of viewport deviceScaleFactor. Adjust one control at a time and compare the resulting PDF; changing device scale factor is not a substitute for setting PDF dimensions.
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The site still renders a desktop layout
Confirm that the viewport or device profile is set before navigation and that the page has loaded under that profile. Device emulation includes more than simply choosing PDF dimensions: a named device profile can also set the user agent. Responsive behavior and viewport metadata on the target site can influence the layout.
The CSS page size seems ignored
Check that preferCSSPageSize: true is set and that the page actually defines a CSS @page size. With the documented default of false, content is scaled to fit the paper size supplied to PDF generation instead of giving the CSS page size priority.
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Performance, reliability, and cost considerations
With a self-hosted Puppeteer workflow, PDF work happens in your browser process: page loading and PDF generation both have to complete successfully for you to receive a file. The settings described here do not establish a universal capture time, reliability rate, or cost per PDF. Those depend on your page, runtime, infrastructure, and workload. For repeatable output, keep the Puppeteer and Chromium versions consistent in the environment that generates the PDFs, and validate after upgrading either.
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Frequently asked questions
Does deviceScaleFactor make text sharper in the PDF?
The documented controls distinguish viewport device scale factor from PDF rendering scale. They do not establish a general rule that increasing device scale factor improves PDF sharpness. Judge the actual output for the target page and PDF options.
Can I use both CSS @page dimensions and PDF dimensions?
You can configure both, but make the intended priority explicit. With preferCSSPageSize: true, the CSS page size takes priority; otherwise the PDF options control the paper size and content is scaled to fit.
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