The limit, and the two rules nobody expects
UKVCAS — the service used for UK visa applications made from inside the UK — sets a limit of 6 MB per file, and states that anything larger will be rejected.
That part is well known. Two other rules in the same instructions catch far more people.
Rule one: dots in the file name
UKVCAS asks for file names that are "as simple as possible", and gives its own example of a name that will cause problems:
"File Name: needs to be as simple as possible e.g. bank-statement-Apr-2018.pdf. Do not upload files with file names having special characters, #, ë, or bank.statement.apr.2018.pdf"
Read the bad example again. It contains no symbols at all — just full stops between the words.
Almost nobody thinks of a dot as a special character. It is also exactly what happens automatically when you export from certain banking apps and document scanners. One applicant on an expat forum reported renaming fifty-five files after discovering this the hard way.
Use hyphens: bank-statement-apr-2018.pdf, not bank.statement.apr.2018.pdf.
Rule two: no password-protected files
UKVCAS asks you not to upload protected files, because the caseworker cannot open them, and says directly that your application may be delayed as a result.
Bank statements are the usual source — many banks issue them password-protected by default, and the file opens perfectly well for you because your browser or reader has remembered the password. Remove the password before uploading, not after a caseworker has queried it weeks later.
The advice UKVCAS gives that is genuinely good
Most portals tell you to "reduce the file size" and leave you to it. UKVCAS is more useful than that:
"To help contain the file size to 6MB please scan in 'Greyscale' or 'Black and white' and not in 'Colour'. It is also helpful to keep the resolution between 150 dpi to 300 dpi... With this approach, you will be able to scan up to 50 pages per document within the allowed 6 MB limit."
This is correct, and it is the same principle this site's compressor is built on.
A colour scan spends its bytes on the paper tint, the shadow where the page met the scanner lid, and sensor noise — none of which a caseworker needs to read. Black and white spends them on the text.
And their number checks out. 50 pages inside 6 MB works out at roughly 120 KB per page. That is almost exactly the figure we measured independently as the point where a greyscale scanned page stays comfortably readable. Two different routes to the same number is a good sign that neither is made up.
If you would rather not rescan everything, the compressor above does the same conversion to the file you already have, and tells you before it runs whether the size you are asking for will still be legible.
Split, do not merge
UKVCAS puts no limit on the number of files and explicitly says to separate anything over 6 MB into parts.
This is worth stating because it is the opposite of what Australia's ImmiAccount wants, where a 60-document cap per person makes merging the right move. Same task, same kind of application, opposite correct answer.
So for a UK application: split the long documents, name each part clearly with hyphens, and upload them separately. Do not spend an evening compressing a 120-page bundle into 6 MB when you were allowed to send it as three files.
If you are applying from outside the UK
You will most likely upload through VFS Global rather than UKVCAS, and the limits are reported to be considerably tighter — figures around 2 MB per file circulate widely.
We have not been able to verify that from an official VFS source, so treat it as a warning rather than a specification: check the limit displayed in your own account before preparing anything. If it is 2 MB, the greyscale advice above matters even more, and splitting becomes essential rather than optional.
The order that saves time
- Remove any passwords first — otherwise you will compress a file you then have to
redo.
- Rename with hyphens, no dots between words.
- Split anything long into parts under the limit.
- Compress to about 5 MB, not 6. Leave the margin.
- Open each file before uploading. A scan compressed past readability is worse than
a large one, because nobody tells you — it simply slows your application down.