400 KB is comfortable for a small colour document, which is usually what arrives here. The tool steps down in three stages and stops at the first that fits.
A colour pair of pages normally settles high on the ladder, meaning the images are barely touched and everything else is left exactly as it was.
A single colour page costs about a quarter of a megabyte and a greyscale one about half that, so 400 KB holds one colour page comfortably, two at a squeeze, or three greyscale. Below that the file is a text document and above it the pages get rebuilt. Knowing which of those you have takes ten seconds and saves a round of guessing.
Where the 400 KB limit comes from
- Recruitment portals taking a document set400 KB per file
- Bank and insurance onboarding uploads300 to 500 KB
- Professional registration and renewals400 KB per certificate
- Consulate and appointment systems400 KB per page
- Grant and bursary applications400 KB per attachment
Round numbers between 200 KB and 1 MB tend to come from somebody who tested the limit against a real document rather than picking a figure. 400 KB is roughly what a scanned two page form weighs at a resolution that stays readable, which makes it one of the more considered caps in the set: tight enough to keep storage down, loose enough that the documents arriving are worth reading.
How the tool hits 400 KB
Add the PDF
A 400 KB cap usually arrives with a small colour document: a two-page scan, or a signed form with a photograph on it. It is read in locally and measured before anything is changed.
Structure, then images that stop high on the ladder
The structural pass is free. The image ladder then runs, and 400 KB is where a colour pair of pages usually sits comfortably at 120 to 150 ppi rather than being pushed to the bottom rungs.
Stage three, rarely reached here
At this size a rebuild is uncommon, and when it happens it usually means the pages are photographs rather than scans. An invisible text layer still keeps anything typed searchable.
Download, and read the result line
It reports size and stage. Stopping in stage two at this target is the normal result, and it means your text never became a picture.
Structure, then the images in place, then the pages as pictures. It stops at the first stage that fits.
Untouched at the first two stages. If the pages do get rebuilt, an invisible text layer keeps them searchable.
The IDs, forms and statements people compress for portals never leave the device.
What fits in 400 KB, and what does not
The arithmetic is the same as everywhere else and the answer is friendlier. Text costs about forty kilobytes a page, a greyscale scan a hundred and thirty, and a colour scan about two hundred and forty. Multiply by your page count before you compress and the result will rarely surprise you.
When it cannot reach 400 KB
400 KB is comfortable for most documents, so a miss means something on the pages is unusually expensive. Three checks:
- Count the colour pages. Two colour pages sit comfortably in 400 KB. Four do not. Knowing which of those you have tells you whether to compress harder or to split.
- Separate the photographs from the text. Use Split PDF to lift out the photographic pages, which are the ones setting the rung for everything else.
- Check the limit before losing quality. A limit stated as 400 KB is often a default that was never revisited. Trying 500 KB costs a moment and may save the detail.
Where the colour pair sits
Two colour pages is the case this cap is really about. One page fits with room to spare and nobody needs a tool. Three or more will not fit in colour at any setting worth using. Two lands almost exactly on the line, which means it is the one document where the settings actually decide the outcome.
What that means in practice is that the result line is worth reading here more than at any other size. If it says the file fitted at 200 ppi, the images were barely touched and the document is as good as it was. If it says 100 or 80, something about the original was heavier than it needed to be, and the likeliest reason is a scanner left at 600 dpi.
The other thing two pages allows that one does not is splitting. Most portals that cap a file at 400 KB accept several files, and two pages at 400 KB each is a better document than two pages sharing 400 KB. Split PDF takes ten seconds and is worth trying before compressing harder.
Where people use the 400 KB target
- Application document sets1 to 2 pages each
- Onboarding paperwork1 page, fits in colour
- Certificates and registrations1 to 3 pages greyscale
- Appointment supporting documents2 pages, borderline
Why this runs in your browser
The documents that meet a 400 KB cap are the ones with your name and number on them: certificates, registrations, identity pages, bank letters. Passing each through an upload-and-download service on the way to a portal doubles the number of copies in existence and gains nothing.
The tool is right above
Everything on this page runs in your browser. Scroll up, drop the file, and keep it on your machine.
Common questions
Questions that come up with a 400 KB cap.
01What fits in 400 KB?
One colour page comfortably, two at a squeeze, three greyscale pages, or six of text. It is the smallest cap where a two page colour document is still realistic.
02My two colour pages just fit. Should I worry?
Read the result line. Fitting at 200 or 150 ppi means the images were barely touched. Fitting at 80 or 60 means the original was much heavier than it needed to be, and a fresh scan would be better than a harder squeeze.
03Would splitting be better than compressing?
Often, yes. Most portals with a 400 KB per file cap accept several files, and two pages at 400 KB each beats two pages sharing 400 KB. Try that before compressing harder.
04Colour or greyscale at this size?
Colour is genuinely affordable here, unlike at 200 KB. Keep it unless the page is dense with small print, in which case greyscale buys resolution that matters more.
05My file is already under 400 KB. Do I need this?
No. The tool checks first and hands a file that already fits straight back untouched.
06Will the text still be selectable?
Almost always. Most documents reach 400 KB in the first two stages, which leave text exactly as it was.
07Are my files uploaded anywhere?
No. Rendering and compression run in your browser. The file never leaves the device.
08Is it free?
Free. Every tool, unlimited use, no signup.