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Start with a reproducible diagnosis
“Too small” can describe different failures: the entire page is uniformly reduced, a wide layout is shrunk to fit, text changes between machines, or the PDF uses the wrong physical sheet. Treat each as a separate variable instead of changing several flags at once.
- Record the complete wkhtmltopdf command, installed binary version, operating system, and build details.
- Save the exact HTML, CSS, and JavaScript fixture and the resulting PDF.
- Write down the intended paper size, margins, physical measurements, expected page count, and the machine that produced the reference output.
- Change one setting, render again, and record the new measurements and page count.
The wkhtmltopdf project describes the tool as an open-source command-line renderer that uses Qt WebKit. Its graphics environment therefore matters even when the process runs without a visible desktop.
Set the PDF paper size explicitly
The default rendered page size is A4. That is not the same thing as the browser window used to lay out the HTML. Use --page-size for a standard sheet, or specify both dimensions for a label, receipt, or other custom stock.
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Standard paper
wkhtmltopdf --page-size A4 input.html output.pdf
wkhtmltopdf --page-size Letter input.html output.pdf
wkhtmltopdf --page-size Legal input.html output.pdfCustom paper
wkhtmltopdf --page-width 100mm --page-height 150mm input.html output.pdfDo not mix an assumed paper size with an unexamined margin configuration. All four margins reduce the width and height available to your content. Set them explicitly when physical placement matters:
wkhtmltopdf --page-size A4
--margin-top 10mm --margin-right 10mm
--margin-bottom 10mm --margin-left 10mm
input.html output.pdfUse the units required by your production specification and keep them identical across environments. If the output is a label or another nonstandard sheet, custom width and height are more reliable than trying to force a standard page to behave like one.
Understand the scale controls
Three settings are commonly confused. The documented defaults are 96 DPI, zoom 1, and smart shrinking enabled.
| Control | What it changes | Useful diagnostic |
|---|---|---|
--dpi |
The rendering DPI used when converting layout units to output. | Test an explicit value when every element is consistently too large or too small. |
--zoom |
A multiplicative zoom applied to the rendered page. | Adjust proportional size after paper geometry is fixed. |
| Smart shrinking | Allows wide content to be scaled down so it fits the printable page. | Compare the default with --disable-smart-shrinking when a wide layout is unexpectedly reduced. |
Test DPI without guessing
A report that --dpi 300 improved one case is a test result, not a universal correction. Build a small matrix around your current command, for example:
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wkhtmltopdf --dpi 96 input.html out-96.pdf
wkhtmltopdf --dpi 150 input.html out-150.pdf
wkhtmltopdf --dpi 300 input.html out-300.pdfMeasure the same feature in each PDF. If only one value matches the physical specification, document why that value is required and keep it in the deployment command. Changing DPI can alter apparent text and image scale; it should not be used as a substitute for selecting the correct paper.
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Use zoom as a separate experiment
With page size, margins, and DPI held constant, test zoom values such as 0.9, 1, and 1.1:
wkhtmltopdf --dpi 96 --zoom 0.9 input.html zoom-09.pdf
wkhtmltopdf --dpi 96 --zoom 1 input.html zoom-10.pdf
wkhtmltopdf --dpi 96 --zoom 1.1 input.html zoom-11.pdfKeep the value that matches the intended physical measurement, not merely the one that looks best at a particular screen magnification.
Check smart shrinking deliberately
Smart shrinking is enabled by default. When a page is wider than the printable area, it can make the whole layout appear smaller. Compare the default with:
wkhtmltopdf --disable-smart-shrinking input.html no-shrink.pdfThe result is layout-dependent. Disabling the feature may preserve the designed scale while introducing horizontal overflow or additional pages, so inspect clipping, line wrapping, and page count after the change.
Keep viewport size separate from paper size
--viewport-size emulates the browser window used for HTML and responsive-CSS layout. It does not choose the physical PDF sheet. A page can use a desktop breakpoint while still being printed on A4, or use a narrow breakpoint while printing on a custom page.
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wkhtmltopdf --viewport-size 1280x900
--page-size A4 input.html output.pdfSet the viewport when your fixture depends on media queries, overflow behavior, or custom scrollbars. Use the width and height that correspond to the intended layout state, then control physical output separately with --page-size, explicit dimensions, and margins.
Account for operating-system and build differences
Identical HTML and nominal flags can produce different apparent scale on different machines. The project’s issue discussion notes that wkhtmltopdf still uses the underlying graphics library in headless operation. Windows display DPI can affect text rendering, while a Linux patched-Qt path in the cited historical environment used a hardcoded assumption.
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- wkhtmltopdf binary version and build (including whether it is a patched-Qt build);
- operating system and architecture;
- Windows display scaling or DPI settings, when applicable;
- fonts installed and available to the rendering process;
- the complete command line and all input assets.
When production must run on a different platform, render the minimal fixture there rather than assuming a workstation result will transfer exactly.
A reliable troubleshooting workflow
- Freeze the fixture. Use one small HTML file with the CSS and JavaScript needed to reproduce the size problem. Keep external assets under the same conditions for every run.
- Fix paper geometry first. Add the intended
--page-size, or both custom dimensions, and explicit margins. - Fix the layout viewport. If responsive rules are involved, add
--viewport-size WIDTHxHEIGHTthat represents the desired browser layout. - Test one scale variable. Run a short DPI matrix, then a zoom matrix. Do not change both in the same experiment.
- Compare smart shrinking. Render once with the default and once with
--disable-smart-shrinkingif wide content is being reduced. - Repeat on the target platform. Include the exact binary and operating-system settings used by the server or build worker.
- Measure rather than eyeball. Check physical dimensions, a known reference element, line wrapping, clipping, and page count after every change.
- Save the winning command. Put the final flags beside the fixture so a later change can be traced to a specific variable.
Diagnose by symptom
Everything is uniformly too small
Confirm the paper size and margins first. Then test explicit DPI and zoom values while leaving all other settings unchanged. A global change points to scale or geometry; changing CSS widths alone may hide the underlying configuration.
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Only wide pages are reduced
Smart shrinking is the first suspect. Compare the default with --disable-smart-shrinking, then inspect the viewport width, printable width after margins, and any fixed-width elements. A no-shrink result that overflows is evidence that the layout is wider than the chosen sheet, not proof that the flag is universally correct.
The same fixture differs between a workstation and a server
Capture the binary version, build, operating system, display-DPI settings, fonts, and complete command from both machines. Re-run a minimal fixture on each. If the difference follows the platform, standardize the rendering environment instead of adding unexplained scale multipliers.
The page count changes after a size adjustment
Recheck margins, smart shrinking, viewport width, and line wrapping. Page count is a useful signal because a setting that makes content physically larger can legitimately push blocks onto additional sheets.
Reference commands
This template makes the principal choices visible for a standard A4 document:
wkhtmltopdf
--page-size A4
--margin-top 10mm --margin-right 10mm
--margin-bottom 10mm --margin-left 10mm
--viewport-size 1280x900
--dpi 96
--zoom 1
input.html output.pdfFor a custom sheet, replace --page-size A4 with --page-width and --page-height. Add --disable-smart-shrinking only when your comparison shows that default shrinking is responsible for the reduction.
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See the ScreenshotNeo API documentation for request options. A basic capture is:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://example.com -o shot.webpThe same request in Python:
import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://example.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)And in Node.js:
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://example.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);ScreenshotNeo also supports PDF output, full-page captures with lazy images loaded, CSS-selector element captures, dark mode, device presets or custom viewports, retina scale, custom CSS and JavaScript, clicks, waits, request blocking, headers, cookies, user agents, authorization, timezone, geolocation, transparent backgrounds, resizing, cache TTLs, signed links, asynchronous jobs with signed webhooks, bulk capture of up to 100 URLs per call, usage reporting, and an MCP server with take_screenshot, get_page_info, and capture_pdf tools for AI clients.
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Frequently Asked Questions
Can ScreenshotNeo replace a local wkhtmltopdf binary for private files?
No. ScreenshotNeo is an HTTP capture service for reachable URLs and supported API inputs, while wkhtmltopdf remains a local command-line renderer. Choose the local binary when the source must stay inside your own environment.
What should I preserve for a future size regression test?
Keep the minimal HTML/CSS/JavaScript fixture, the exact command, binary version and build, operating-system details, expected physical dimensions, and a known output PDF together.
Is 300 DPI the correct permanent setting?
Not automatically. It improved one reported case, but DPI is a configuration variable; select it only after measuring your own fixture against the required physical dimensions.
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