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JPG to PDF under 40 KB

To make a PDF under 40 KB, PixelFit compresses the JPG to at most 39,264 bytes and wraps it in a one-page PDF with about 736 bytes of PDF structure, 40,000 bytes or less in total. Measured: an A4 scan fits up to 60 DPI at quality 50; a 4:3 photo at about 451 × 338 pixels (quality 75).

PDF under 40 KB

PDF · under 40 KB (at most 40,000 bytes) · original pixel size · white background

PixelFit aims at 40,000 bytes or less, so the file passes whether the form counts 1 KB as 1,000 or 1,024 bytes.

Fit, background and padding white background · page the size of the picture

Saving presets is part of Pro.

Pick a photo to fit it to under 40 KB (at most 40,000 bytes).

The result appears here: the exact byte count, pixel size and quality, the size before and after, a preview and a download button.

Where the 40 KB go in a JPG-to-PDF file

Of the 40,000 bytes that pass as 40 KB under both KB definitions, PDF structure takes 736 bytes for one A4 page (computed with PixelFit's own writer), leaving 39,264 bytes, 98.1 %, for the JPEG; ten pages leave 3,476 bytes each.

For one photo, quality 75 allows 451 × 338 pixels and quality 90 349 × 261; a full 12 MP frame must be scaled down first, which the tool does for you.

How many pages fit in a 40 KB PDF

The 40,000 bytes of 40 KB, less 736 bytes of PDF structure for the first page and about 500 for each extra one, shared evenly.

PagesJPEG bytes per pageMax A4 DPI at q50Max A4 DPI at q75A4 at 150 DPI
1 page 39,264 60 DPI 48 DPI no: 3.2× over at q30
2 pages 19,384 41 DPI 33 DPI no: 6.5× over at q30
3 pages 12,755 33 DPI 27 DPI no: 9.8× over at q30
5 pages 7,453 26 DPI 20 DPI no: 16.8× over at q30
10 pages 3,476 17 DPI 13 DPI no: 36.0× over at q30

Make a PDF under 40 KB →

Phone photos in one PDF under 40 KB

Largest 4:3 photo per page, in pixels, when 1 to 10 photos share 40,000 bytes; "full" means a 12 MP phone photo keeps all its pixels (the tool never enlarges).

Width × height in pixels. * = outside the measured range (100 to 3000 px long edge), extrapolated.
PhotosQuality 60Quality 75Quality 90
1 photo 522 × 391 451 × 338 349 × 261
2 photos 363 × 272 311 × 233 241 × 180
3 photos 290 × 217 251 × 188 193 × 144
5 photos 219 × 164 187 × 140 143 × 107
10 photos 139 × 104 119 × 89 91 × 68*

A4 and Letter pixel sizes against 40 KB

One typed page per DPI: its pixels, the quality it gets alone in 40 KB, and how many fit at quality 75.

DPIA4 pixelsOne A4 page under 40 KBLetter pagePages at q75
72 DPI 595 × 842 quality 31 quality 33 none
100 DPI 827 × 1169 no: 1.7× over at q30 no: 1.7× over at q30 none
150 DPI 1240 × 1754 no: 3.2× over at q30 no: 3.1× over at q30 none
200 DPI 1654 × 2339 no: 4.8× over at q30 no: 4.7× over at q30 none
300 DPI 2480 × 3508 no: 8.6× over at q30 no: 8.4× over at q30 none

Readable pages and photos in 40 KB

40 KB holds a full typed A4 page only as a low-resolution scan: about 60 DPI (496 × 702 pixels) at quality 50, where a line of 12-point type is about 10 pixels tall, hard to read. A 72 DPI scan (595 × 842) fits only at quality 31, below our threshold of 50.

What fits at a readable 150 DPI is a crop: a full-width strip about 49 mm high (16 % of the page, roughly 9 lines of 12-point type at single spacing) at quality 50. For a certificate or mark sheet, crop to the part the form needs before you convert.

Under 40 KB a full 150 DPI A4 scan gets nothing: even quality 30 is 3.2 times too big, and no photo of 1600 × 1200 fits at quality 70.

One image free, several merged with Pro

Free: each image becomes its own one-page PDF under 40 KB. Pro: several images merged into one PDF under 40 KB, on your device; 2 pages get 19,384 bytes of JPEG each.

How to turn a JPG into a PDF under 40 KB

  1. Open the tool above

    Preset: PDF output, at most 40 KB.

  2. Add the JPG

    Drop, paste or pick it (PNG, WebP and HEIC work too).

  3. Choose the page

    Keep the picture's own size or fit it on A4 or Letter.

  4. Download

    name-40kb.pdf arrives with its exact byte count (40,000 bytes or less).

Sources

  1. Measured by PixelFit with sharp 0.35.5 / libvips 8.18.7 on 31 October 2026.
  2. Samples, Wikimedia Commons, checked 31 October 2026: typed page (public domain) commons.wikimedia.org/w/index.php?curid=194775753; landscape (CC0 1.0) commons.wikimedia.org/w/index.php?curid=154070378
  3. Paper sizes, Markus Kuhn, checked 31 October 2026: cl.cam.ac.uk/~mgk25/iso-paper.html
  4. PDF format, Library of Congress, checked 31 October 2026: loc.gov/preservation/digital/formats/fdd/fdd000474.shtml

Frequently asked questions

How do I convert a JPG to PDF under 40 KB?

Drop the JPG into the tool on this page, preset to PDF under 40 KB: the picture is compressed to 39,264 bytes or less, so the PDF ends at or below 40,000 bytes.

Can I convert JPG to PDF for free?

Yes, one image per PDF, with no upload. Under 40 KB a 4:3 photo keeps 451 × 338 pixels at quality 75; merging several JPGs is Pro.

How many pages fit in a 40 KB PDF?

Under 40 KB, not even one full A4 page at 150 DPI keeps quality 50; a whole page fits only at about 60 DPI, so crop to the part you need (a full-width strip about 49 mm high at 150 DPI).

What DPI should a scan have for a 40 KB PDF?

None of the usual 72 to 300 DPI settings keeps a full A4 page at quality 50 under 40 KB: the limit is about 60 DPI. Scan at 150 DPI and crop to the needed part instead.

Why is the PDF bigger than my JPG?

A PDF wraps the JPEG in page, image and cross-reference objects: 736 bytes for one page in PixelFit's writer, about 500 more per added page.

Related

Other PDF size limits

More for 40 KB

Pixel sizes that fit 40 KB

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