Prepare a PDF for fax: black and white, resolution, size

Short answer: lay each page flat on the scanner, choose a black-and-white setting with 200 dpi resolution, use letter-size pages, and keep the file light. A fax machine converts anything you send into a bi-level image of roughly 200 by 100 dots per inch (standard) or 200 by 200 (fine). The cleaner and darker your source, the better the printed result.

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A fax is a very old format and it is unforgiving. Color disappears, pale pencil vanishes, tiny print blurs into a gray smudge. Online services accept PDFs, photos and office files and convert them for you, but conversion cannot invent detail that was never in the file. A few minutes of preparation make the difference between a page the recipient reads at once and one they call you about.

What the fax network actually sends

Classic fax transmits each page as a series of black or white dots. There is no gray and no color. Your document is therefore reduced to two tones before it leaves.

• Standard mode uses about 204 × 98 dpi, enough for typed text of 11 points and above.
• Fine mode uses about 204 × 196 dpi, better for small print and forms.
• Page size is Letter in North America (8.5 × 11 in) or A4 elsewhere; the converter fits your pages to it.

The consequence is simple: design the document for black ink on white paper, as if you were going to photocopy it.

A five-step checklist

1. Scan, do not photograph, when you can. A flatbed or a sheet-fed scanner gives even light and straight edges. A portable document scanner is enough for a home office and fits in a drawer.
2. Choose black and white (or "text") mode, 200 dpi. Higher resolutions only increase file size; the fax network will reduce them anyway. If your scanner offers "document" or "text" enhancement, enable it: it sharpens edges.
3. Raise the contrast. Pale gray text, stamps in color and signatures in light blue ink disappear. Re-sign with a black pen if the original is faint.
4. Crop and straighten. Black borders and slanted text waste space and can trigger page-skew errors. Most scanning apps offer automatic crop.
5. Check the result at actual size. Zoom to 100 percent and read the smallest line. If you struggle, the recipient will too.

Fonts and layout for documents you create

If you write the document yourself, a few choices make a fax-friendly page.

• Use a plain font in at least 11 points; avoid thin or decorative typefaces.
• Black text on a white background. Skip shaded boxes, watermarks and colored table rows: they turn into gray noise.
• Leave a half-inch margin on all sides; some machines clip the edge.
• Put the recipient's name and the page count at the top of page one. The free cover-page generator produces a ready cover sheet.

File size and format

Web services take PDF, Word, Excel, pictures and plain text files of up to 100 MB each, and they convert whatever is not already a PDF. A few cautions:

• Keep it as a PDF. A conversion from an office format occasionally shifts fonts or page breaks. Export to PDF first, check it, then upload.
• Remove unnecessary pages. The price depends on length, and every extra page is also an extra minute of transmission.
• Avoid password-protected PDFs. They cannot be converted.
• Flatten forms. Fillable fields should be printed to PDF so the filled values appear.

The price calculator tells you what a document of a given length will cost before you start.

Handy kit for people who fax occasionally

None of this is essential, but a few inexpensive items save time. A small sheet-fed scanner beats photographing pages one by one, and a ream of clean white letter-size copier paper avoids the show-through that darkens a scan. If you still use a machine, keep spare thermal fax paper in the drawer.

Frequently asked questions

Can I fax a color document?

Yes, but the recipient receives it in black and white. Check that nothing important depends on color.

Is a photo from my phone good enough?

For a quick one-page job, yes, if you shoot in daylight, flat and straight on, with the page filling the frame. For anything long or small-print, scan instead. More in fax from a phone.

Why did my fax come out dark?

Usually a gray background on the original or a shadow in the photo. Raise contrast, or rescan on a brighter surface.

What file size is too large?

The limit is 100 MB, but a scan above 10 MB for a few pages is a sign the resolution is too high.

Key points

• Scan flat, black and white, 200 dpi, then check at 100 percent.
• Black on white: avoid color, shading and pale ink.
• Export office files to PDF first and verify them.
• Finish with a cover page naming the recipient and the number of pages.