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Your file is too big for the upload form — here's what to do

A decision guide for PDFs, photos and scans a form refuses: what actually makes each file heavy, what to try first, and the shortcuts that do not work.

· 6 min read

Start from what kind of file it is, not from how many megabytes it has. A photo is heavy because of its pixel count, a scanned PDF because of the images inside it, and a long report because of one embedded picture. The right fix is different in each case, and it is almost never "compress harder".

The quickest route here: photos go to Compress image with the maximum width set to 1920 px; PDFs go to Compress PDF at the recommended level; and when a form states an exact figure such as "under 200 KB", use Resize image in KB, which searches for the highest quality that still fits.

Start with the right question

Your file What makes it heavy Try first
A phone or camera photo The number of pixels Resize image to 1600–1920 px
A photo that must hit an exact limit — Resize image in KB
A screenshot saved as PNG Lossless storage of every pixel Convert to JPG with Image converter
A scanned PDF The scan images inside it Compress PDF, recommended level
A PDF exported from a document Embedded photos and logos Compress the images, then re-export
A very long PDF Page count Split PDF and send it in parts

The limits you are actually hitting

Web forms commonly cap uploads at 2 MB or 5 MB, and government and exam portals are often stricter still. Email is a separate system with its own ceilings: Gmail refuses attachments over 25 MB and offers a Drive link instead, Outlook.com currently caps a message at 20 MB, and a company mail server is whatever the administrator configured — frequently less.

One detail catches people out. Attachments are encoded in base64 for transport, which makes them roughly a third larger in the message than they are on disk. A 20 MB file becomes about 27 MB of message, which is why a "25 MB limit" can reject a 20 MB attachment.

For photos, resize before you compress

Lowering the JPEG quality is the obvious lever and the weaker one. Pixels are what cost bytes: a 4000 × 3000 photo holds 12 million of them; at 1920 × 1440 it holds 2.8 million — about a quarter as many — and it still fills any laptop screen edge to edge. Resize first, then lower the quality if you still need to.

Going the other way, pushing quality below about 60 produces visible blocks around text and edges. That is exactly what makes a scanned ID unreadable to the person reviewing it, and it is the reason a file can pass the size check and still be refused on content.

A PNG screenshot is a special case: PNG stores every pixel exactly, so a full-screen capture can easily reach several megabytes. Converting it to JPG usually removes most of that, at the cost of slightly fuzzier text.

For scanned PDFs, expect a big win

A colour A4 page scanned at 600 DPI can weigh several megabytes on its own. Strong compression re-renders each page as an image at 80–150 DPI, which is plenty for reading on screen, and often divides the size by five or ten.

The trade-off is real and worth stating plainly: the text becomes part of the image, so it can no longer be selected, searched or copied, and it cannot be turned back. For a contract you will need to quote from, keep the lossless option or the original. For a proof of address that someone will glance at once, strong compression is the right call.

If the document is simply long, Split PDF cuts it into parts by page range without re-compressing anything — quality and selectable text are preserved, and each part goes under the limit on its own.

When the form still says no

Check the other requirements before compressing again. Portals frequently impose several at once:

  • an exact format (JPG only, or PDF only);
  • fixed pixel dimensions, for example 600 × 800 for a photo;
  • a minimum size as well as a maximum — 20 KB to 50 KB is a common range;
  • a maximum number of pages;
  • a file name without spaces or accented characters.

A file that meets the size limit but not the dimensions is rejected with the same unhelpful message. And if the upload is a HEIC photo straight from an iPhone, the format is the problem, not the size: browsers cannot decode HEIC, so most portals refuse it. Set Settings → Camera → Formats to "Most Compatible", or export a JPEG copy first.

What not to do

Don't rename the extension. Renaming photo.png to photo.jpg changes nothing inside the file; a well-built form reads the file's header and rejects it.

Don't compress the same file twice. Each JPEG pass re-encodes what the previous one already degraded. Two passes at quality 80 look worse than one pass at 70 and are rarely smaller. Go back to the original.

Don't zip it. PDFs, JPGs and PNGs are already compressed, so a ZIP saves almost nothing, and most forms will not accept an archive.

Don't screenshot a PDF to make it smaller. You lose the text layer and usually gain size.

What the built-in apps can do

  • Windows Photos resizes through "Resize image" in the "See more" menu, with pixel dimensions and a quality slider. It cannot aim at a size in KB.
  • macOS Preview resizes with Tools → Adjust Size and re-encodes with File → Export, where the quality slider shows the resulting size as you drag it. Its PDF export also offers the "Reduce File Size" Quartz filter, which is aggressive and can soften text noticeably.
  • iPhone Photos cannot resize to pixel dimensions. Mail offers Small, Medium, Large or Actual Size when you attach a photo, which is a resize in disguise.
  • Android Google Photos edits and crops; resizing depends on the manufacturer's gallery app, so it is not something to count on.

Questions people ask

How small should I aim for? Just under the stated limit, not as small as possible. Over-compressing is how a legible document becomes an illegible one.

Will compressing a PDF remove the password? No. An encrypted PDF has to be decrypted before any tool can read its pages.

Is 1 KB 1000 or 1024 bytes? Both conventions exist. Windows counts 1 KB as 1024 bytes, macOS displays 1 MB as 1,000,000 bytes, and most upload forms use 1024 — the safer assumption when a limit is tight.

Does compressing remove the photo's location data? Yes, re-encoding drops EXIF, including GPS coordinates.

Are my files uploaded anywhere? Not with these tools. They run in your browser, which is why identity documents and contracts stay on your device.

Next steps

Tools used in this guide

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