KB to MB Converter

Divide by a thousand — and find out whether that file will actually fit in an email.

Conversion table

Size	In megabytes
1	0.001 MB
2	0.002 MB
3	0.003 MB
4	0.004 MB
5	0.005 MB
10	0.01 MB
15	0.015 MB
20	0.02 MB
25	0.025 MB
30	0.03 MB
40	0.04 MB
50	0.05 MB
60	0.06 MB
70	0.07 MB
75	0.075 MB

📁 What things weigh

1 MB1,000 KB
A text document20–100 KB
A phone photo3,000–6,000 KB
Gmail attachment cap25,000 KB

Getting a file under the limit

Attachments are encoded in base64 for transport, which inflates them by about a third. A 20 MB file can therefore fail a 25 MB limit.
Photos are the usual culprit. Exporting a phone photo at 2,000 px wide instead of full resolution typically cuts it from 4 MB to under 500 KB.
A PDF full of scanned pages shrinks dramatically when the images are downsampled to 150 dpi — often by 80% with no visible loss on screen.
If it still will not fit, send a link. Gmail does this automatically above 25 MB by uploading to Drive.

A thousand kilobytes, or 1,024 of them

In the decimal system used by storage makers, networks and this converter, a megabyte is exactly 1,000 kilobytes, so 5,000 KB is 5 MB and 250 KB is 0.25 MB. File managers usually do the arithmetic in binary instead, dividing by 1,024, and then print the result labelled MB — which is why a file your operating system calls 4.88 MB is described as 5,000 KB elsewhere. The difference is 2.4% per step, small enough to ignore for an email and large enough to notice on a full disk.

Why the attachment limit is not the file size

Email was designed for plain text, so binary attachments are re-encoded in base64 before they travel, and base64 uses four characters for every three bytes. That is roughly a 33% increase, before headers. A 20 MB file therefore arrives at the server as about 27 MB of message and bounces off a 25 MB ceiling that it looked like it should clear. Gmail's published limit is 25 MB for the whole message; many corporate servers stop at 10 MB, and the recipient's limit matters as much as yours.

Real file sizes, so you can estimate

Plain text: about 1 KB per 500 words. A whole novel in plain text is under 1 MB.
A word processor document of ten pages, text only: 20–100 KB.
A phone photo: 3,000–6,000 KB. A camera RAW file: 25,000–50,000 KB.
A colour PDF scan: roughly 500 KB per page at 300 dpi, a tenth of that at 150 dpi.
A three-minute MP3 at 192 kbps: about 4,300 KB.
A minute of 1080p video: 50,000–100,000 KB, which is why video never survives an email.

How to make a file smaller

Resize before compressing. Halving both dimensions removes three quarters of the pixels and usually four fifths of the file.
JPEG at quality 80 is visually indistinguishable from 100 for most photos and roughly a third of the size.
Use PNG only for graphics with flat colour and text; a photo saved as PNG can be five times larger than the same JPEG.
Zipping a JPEG or an MP4 saves almost nothing — those formats are already compressed.
Zipping many small text or office files does help, often by 60–80%.
For anything over 25 MB, a shared link is faster for both sides and leaves the recipient's inbox alone.

Worked examples

Checking a file against a limit

A 4,800 KB photo

4,800 ÷ 1,000 = 4.8 MB
Base64 encoding adds a third: about 6.4 MB of message
Comfortably under a 25 MB cap, but tight against a 10 MB one with three attached

4,800 KB = 4.8 MB

A 25,000 KB presentation

25,000 ÷ 1,000 = 25 MB
After base64 the message is about 33 MB
It will bounce off Gmail's 25 MB limit — send a link instead

25,000 KB = 25 MB, too big to attach

Frequently Asked Questions

How many KB are in an MB?

1,000 in the decimal system used here, by storage manufacturers and by networks. Your file manager may divide by 1,024 instead and still print MB, so the same file can be described as 5,000 KB in one place and 4.88 MB in another. Both are counting the same bytes.

Is 5000 KB the same as 5 MB?

Yes in decimal, which is how file sizes are usually quoted. In the binary counting that Windows uses, 5,000 KB comes out as 4.88 MB — the figures differ by 2.4% because that system divides by 1,024. Nothing has changed about the file.

Why is my 20 MB attachment rejected by a 25 MB limit?

Because email re-encodes attachments in base64 before sending, which adds about a third to their size. A 20 MB file becomes roughly 27 MB of message, plus headers, and that is what the server measures against its limit. Two 10 MB files will fail a 25 MB cap for the same reason.

How big can a Gmail attachment be?

25 MB for the whole message, which includes every attachment and the base64 overhead. Above that, Gmail uploads the file to Drive and sends a link instead. Remember the recipient's server has its own limit, and many corporate systems stop at 10 MB.

How do I shrink a photo that is too large to email?

Resize it before compressing. Exporting at 2,000 pixels on the long edge and JPEG quality 80 typically takes a 4 MB phone photo below 500 KB with no visible difference on a screen. Zipping it instead saves almost nothing, because JPEG is already compressed.

Why does my file manager show a different size than the website did?

Two reasons. It may be counting in binary, dividing by 1,024 rather than 1,000, and it may be reporting size on disk rather than size of the file — small files still occupy a whole allocation unit, often 4 KB, so a 1 KB file can be listed as taking 4 KB of space.