How much smaller will it get?

Often substantially — colour images carry three channels and greyscale carries one.

Does it convert coloured charts?

Not vector graphics, only images. Text and vectors are left alone deliberately; rewriting every content stream risks breaking the document.

No. The colour information is discarded rather than hidden.

Should I just use my printer settings?

If you are printing yourself, yes — it is free. Convert when the file is going to someone else.

Convert a PDF to greyscale — Free, no signup

Convert a PDF to greyscale

Turn a colour PDF black and white — smaller files and cheaper printing.

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This tool needs JavaScript, because the work happens on your own device rather than on a server. Everything below — the guide and the answers — works without it.

Why people do this

Printing cost, mostly. Colour printing at a shop or an office charge-back is several times the price of monochrome, and a hundred-page document with a colour logo on every page is billed as a hundred colour pages. Converting first can be the difference between a few rupees and a few hundred.

The other reason is size. Colour images carry three channels; greyscale carries one, so the file usually shrinks substantially.

What gets converted, and what does not

Every embedded image becomes greyscale. Text and vector graphics are left alone — and that is a deliberate decision worth explaining.

A PDF's text is almost always already black. Its vector colour lives in operators scattered through the page's content streams, and rewriting those reliably means parsing and regenerating every stream in the document, which risks breaking it for very little gain. The images are where both the colour and the file size actually are.

So if your document is text with photographs, this does exactly what you want. If it is a chart built from coloured vector shapes, those keep their colour — and your printer's own greyscale mode will handle them at print time.

It is not reversible

Colour information is discarded, not hidden. Keep the original if you may need it.

Print settings versus converting

Most printer drivers have a greyscale option, which costs nothing and changes no file. Convert here when the document is being sent somewhere — to a print shop, or to someone whose settings you do not control.