When a PDF under 100 KB helps
- A single scanned certificate or ID page for an upload form
- One-page letters with a logo or a scanned signature
- Receipts and forms photographed with a phone
Send one page if you can. Every extra page splits the same 100 KB, as the table below shows. Cut out the page you need first, then compress that file.
A 12-megapixel phone photo saved as a PDF page has 4,032 × 3,024 pixels, while a Letter page at 150 dpi has 1,275 × 1,650. The tool scales such images down to the page before it saves them again as JPEG, so a photographed document has a lot to gain.
Budget per page at 100 KB
100 KB is 100,000 bytes, or 800,000 bits, for the whole file: every page, image and font and the structure that holds them together. For a scanned document almost all of it goes to the page images. One Letter page at 150 dpi, the Medium level, has 2,103,750 pixels, so a one-page scan gets 0.38 bits per pixel at 100 KB.
| Pages | Per page | Good0.5 bits per pixel | Moderate0.25 bits per pixel |
|---|---|---|---|
| 1 | 100 KB | 120 dpi | 150 dpi |
| 5 | 20 KB | 50 dpi | 72 dpi |
| 10 | 10 KB | below 50 dpi | 50 dpi |
| 20 | 5 KB | below 50 dpi | below 50 dpi |
The last two columns show the highest resolution on the tool's list at which a full scanned Letter page still gets that many bits per pixel. Quality bands from section 4.5 of Gregory Wallace's paper on the JPEG standard, which rates color images of moderate detail; he notes that results vary with the content, so read them as a cautious guide for scans. A4 is about 3% larger than Letter.
The steps the tool tries for 100 KB
The tool does not guess from a table: it compresses the real file and measures it. These are its ten steps, from mild to strong, with the pixel size of a full Letter page at each resolution and the number of such page scans that 100 KB holds at 0.5 bits per pixel.
| Step | Resolution | JPEG quality | Letter page | Full pages at 100 KB |
|---|---|---|---|---|
| 1 | 300 dpi | 85 | 2,550 × 3,300 | not one full page |
| 2 | 200 dpi | 80 | 1,700 × 2,200 | not one full page |
| 3 | 150 dpi | 72 | 1,275 × 1,650 | not one full page |
| 4 | 150 dpi | 60 | 1,275 × 1,650 | not one full page |
| 5 | 120 dpi | 55 | 1,020 × 1,320 | 1 page |
| 6 | 100 dpi | 50 | 850 × 1,100 | 1 page |
| 7 | 85 dpi | 45 | 723 × 935 | 2 pages |
| 8 | 72 dpi | 40 | 612 × 792 | 3 pages |
| 9 | 60 dpi | 35 | 510 × 660 | 4 pages |
| 10 | 50 dpi | 30 | 425 × 550 | 6 pages |
Which PDFs fit in 100 KB
A one-page scan keeps 0.5 bits per pixel, which Wallace's guide rates good to very good, up to 120 dpi. Ten scanned pages fall below 0.5 bits per pixel at every step, so 100 KB suits a few pages better than a long scan. A PDF of text, like a letter or an invoice exported from a word processor, has no page images, so it fits or not depending on its fonts and text, and this tool copies those unchanged.
Some images stay as they are, because recompressing them would change them or gain nothing: images under 12 KB (12,288 bytes), black-and-white scans stored with fax-style compression (CCITT or JBIG2), JPEG 2000 images, images with a stencil or color-key mask, CMYK images, and flat graphics like logos and charts unless they shrink a lot in pixels. A recompressed image also has to be at least 10% smaller than the original, or the original is kept.
When 100 KB is out of reach
- If the PDF is already at or under 100 KB, the tool says so and you can send the original as it is.
- If it has no images the tool can recompress, it tells you right away that 100 KB is out of reach.
- If even the strongest step, 50 dpi at JPEG quality 30, stays above 100 KB, you see the smallest size it reached. When text, fonts and other parts alone take more than 100 KB, the message says how much. If that smallest version is at least 3% smaller than the original, you can still download it.
Then send fewer pages or split the document: cut out pages with Split PDF or drop the ones you do not need with Delete PDF Pages, and compress each part.
100 KB in bytes
The tool counts 100 KB as 100,000 bytes and stays at or under that. Counted in units of 1,024 bytes, the same limit is 97.66 KB or 0.095 MB, so the file also passes a form that counts that way.
Getting a PDF under 100 KB
Drop a PDF above. The target is already set to 100 KB. Press Compress PDF and the tool first runs its strongest step to check that 100 KB can be reached. If it can, it searches its steps for the mildest one that fits, from 300 dpi at quality 85 down, which takes three or four more runs. Text, fonts, links and form fields are copied unchanged. When the result uses 72 dpi or less, the tool asks you to zoom in and check that scanned text is still easy to read.
Need a different limit? One size up is 200 KB. Type any size into the target field, or use the PDF compressor with Low, Medium or High compression. To combine files first, use Merge PDF; to turn photos of a document into a PDF, JPG to PDF. For a photo or a scan saved as an image, compress the image to 100 KB instead.
Sources
Frequently asked questions
How many scanned pages fit in 100 KB?
At 0.5 bits per pixel, which Wallace's guide rates good to very good for color images, 100 KB holds not one full page scanned at 150 dpi, 1 page at 100 dpi and 3 pages at 72 dpi (US Letter; A4 is about 3% larger). Fonts and the file structure take part of the budget too. These are estimates: the tool measures the real file at each step and keeps the mildest one that fits.
Why does my PDF stay above 100 KB?
Because the tool only recompresses images. Text, fonts, vector drawings and the structure of the file are copied unchanged, and if those alone take more than 100 KB, no image setting gets the file under the limit. The result then says how much those parts take. Sending fewer pages or splitting the PDF is the way out.
Will a scanned page still be readable at 100 KB?
Often it will for a single page, but check the result. The tool picks the highest resolution on its list that fits, from 300 dpi down to 50 dpi. When it ends at 72 dpi or less, it tells you to zoom in and check that the scanned text is still easy to read.
Is my PDF uploaded to compress it to 100 KB?
No. Your browser opens the PDF, recompresses the images in it and writes the new file on your own device. Nothing is sent to a server.