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Converting a PDF to grayscale replaces every colour with a shade of grey using the BT.709 luminance formula, so text stays sharp and photos keep their contrast. A grayscale PDF prints without touching colour ink or toner, satisfies portals that require black-and-white submissions, and is usually far smaller than the colour original. PDFWix converts each page in your browser at 150 DPI, 300 DPI or high-contrast black and white.
Converting a PDF to grayscale replaces every colour with a shade of grey using the BT.709 luminance formula, so text stays sharp and photos keep their contrast. A grayscale PDF prints without touching colour ink or toner, satisfies portals that require black-and-white submissions, and is usually far smaller than the colour original. PDFWix converts each page in your browser at 150 DPI, 300 DPI or high-contrast black and white.
| Method | Colour removed from file | Same result on every printer | Smaller file | Text stays selectable |
|---|---|---|---|---|
| PDFWix Grayscale PDF | ✓ Yes | ✓ Yes | Usually yes | ✗ No |
| Printer greyscale setting | ✗ No | ✗ Depends on driver | ✗ No | ✓ Yes |
| Screenshot each page | ✓ Yes | ✓ Yes | ✗ Often larger | ✗ No |
| [compress PDF online](/compress-pdf) | ✗ No | n/a | ✓ Yes | ✓ Yes |
Why converting the file differs from ticking greyscale in the print dialog.
To convert a PDF to grayscale free: open PDFWix Grayscale PDF, drop in the file, pick Standard 150 DPI, High-resolution print 300 DPI or high-contrast scanned document, then click Convert to Grayscale and download. Every page becomes black and white, so printing uses no colour ink. Conversion runs in your browser.
PDFWix Grayscale PDF renders each page with pdf.js, converts the pixels using the ITU-R BT.709 luminance formula (Y = 0.2126R + 0.7152G + 0.0722B), and rebuilds the document with pdf-lib at the original page dimensions. Presets render at 150 DPI, 300 DPI, or 200 DPI with a luminance threshold for scanned paperwork. Because pages are re-drawn as images, text is no longer selectable in the output. All processing happens in the browser.
Greyscale is not simply "colour turned off". Each pixel's three colour channels are collapsed into a single brightness value using the BT.709 luminance weights — roughly 21% red, 72% green, 7% blue — which match how human vision responds to each channel. A naive average would turn red headings into muddy mid-grey and wash out yellow highlights; luminance weighting keeps coloured text and chart lines distinguishable from the page behind them. The trade-off is worth knowing before you convert. PDFWix re-draws every page as a grayscale image and rebuilds the PDF at the original page size, which guarantees that no colour survives anywhere in the file — including inside embedded images, logos and background tints that colour-managed printers otherwise reproduce with coloured toner. Because the page becomes an image, the text in the output is no longer selectable or searchable, so keep the colour original if you still need to copy from it. Pick 300 DPI whenever the file will be printed and read closely; 150 DPI is plenty for screen reading and everyday office printing, and produces a much smaller file.
Presets: 150 DPI · 300 DPI · high contrast · Colour left in the file: None · Processing: 100% in your browser
If your goal is purely a smaller file rather than black and white, try Compress PDF first — it keeps colour and keeps text selectable.
Yes. PDFWix converts PDFs to grayscale for free with no watermark on the output.
Yes. There is no colour data left in the file, so even a colour printer uses only the black cartridge.
Usually. At 150 DPI the file is typically smaller than the colour original; at 300 DPI it may be similar in size but far cheaper to print.
No. Pages are re-drawn as grayscale images, so text becomes part of the picture. Keep the colour original if you need selectable text.
Grayscale keeps shades of grey, so photos still look natural. The high-contrast preset forces pure black or white, which suits scanned text and line drawings.
150 DPI for screen reading, email and everyday office printing; 300 DPI when the document will be printed and read closely, such as a filing or thesis.
No. Rendering and conversion happen inside your browser, so the PDF stays on your device.
Yes, in any modern mobile browser. Very long documents at 300 DPI are faster and more reliable on a desktop.
If you only need a smaller file, start with reduce PDF size. To save individual pages as images instead, convert PDF to JPG, and to combine several documents before converting use Merge PDF.