Compress PDF to 1 MB

Where a 1 MB PDF limit applies

For passport applications through its applicant portal, the Consulate General of India in Lagos asks for documents in PDF format of at most 1 MB, and says the total of all uploaded documents should not be more than 1 MB. Up to 5 documents, including the photograph and signature, can be uploaded per application. Source: Consulate General of India, Lagos: SOP for document uploading in the applicant portal (passport applications).

• Passport, visa and residence permit documents
• CVs with a photo and portfolios for job portals
• Scanned contracts and statements for banks and landlords

A limit on the total of all files is stricter than it looks. If three PDFs have to fit into 1 MB together, each one gets about 333 KB, so compress each file to its share rather than to 1 MB.

For a PDF of several megabytes, look at the share of images the tool shows when you drop the file. A long report that is mostly text and vector charts may not reach 1 MB, and then splitting it is the way out.

Budget per page at 1 MB

1 MB is 1,000,000 bytes, or 8,000,000 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 3.8 bits per pixel at 1 MB.

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 1 MB

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 1 MB holds at 0.5 bits per pixel.

Which PDFs fit in 1 MB

A one-page scan keeps 0.5 bits per pixel, which Wallace's guide rates good to very good, up to 300 dpi. Ten scanned pages still get there at 120 dpi. 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 1 MB is out of reach

• If the PDF is already at or under 1 MB, 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 1 MB is out of reach.
• If even the strongest step, 50 dpi at JPEG quality 30, stays above 1 MB, you see the smallest size it reached. When text, fonts and other parts alone take more than 1 MB, 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.

1 MB in bytes

The tool counts 1 MB as 1,000,000 bytes and stays at or under that. Counted in units of 1,024 bytes, the same limit is 976.56 KB or 0.954 MB, so the file also passes a form that counts that way.

Gmail allows 25 MB per message for personal accounts. Attachments travel Base64 encoded, which turns every 3 bytes into 4 characters, so a 1 MB PDF takes about 1,333,336 bytes in the message. That makes 18 or 19 such files per message, depending on whether 25 MB means 25,000,000 or 25 × 1,048,576 bytes. Counting the plain files instead gives 25 or 26.

Getting a PDF under 1 MB

Drop a PDF above. The target is already set to 1 MB. Press Compress PDF and the tool first runs its strongest step to check that 1 MB 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 down is 500 KB, one size up 2 MB. 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 1 MB instead.

Sources

• Consulate General of India, Lagos: SOP for document uploading in the applicant portal (passport applications)
• Gmail Help: attachment size limits
• RFC 2045, section 6.8: Base64 content-transfer-encoding
• Gregory K. Wallace: The JPEG Still Picture Compression Standard, section 4.5 (copy hosted by the National University of Singapore)

Frequently asked questions