Is 100 KB 100,000 or 102,400 Bytes?
Updated 11 November 2026 · Metro Research editorial team · How we test
Your computer says the file is 99 KB. The form says the limit is 100 KB. The upload is still rejected. The usual cause is that the two systems count a kilobyte differently.
Two definitions of a kilobyte
The decimal kilobyte (kB) is 1,000 bytes. The binary kilobyte, formally a kibibyte (KiB), is 1,024 bytes. Windows File Explorer reports sizes in binary units but labels them “KB”; macOS reports decimal units. Websites can use either.
| Limit shown | Decimal (bytes) | Binary (bytes) | Difference |
|---|---|---|---|
| 20 KB | 20,000 | 20,480 | 480 |
| 50 KB | 50,000 | 51,200 | 1,200 |
| 100 KB | 100,000 | 102,400 | 2,400 |
| 200 KB | 200,000 | 204,800 | 4,800 |
| 500 KB | 500,000 | 512,000 | 12,000 |
| 1 MB | 1,000,000 | 1,048,576 | 48,576 |
How to stay safe
- Assume the stricter decimal limit unless the destination says otherwise.
- Aim a little below the limit; a file at 98,000 bytes passes both definitions of 100 KB.
- Check the exact byte count, not the rounded size your computer shows.
Metro Research's File Studio defaults to the strict 1 KB = 1,000 bytes and shows the exact byte count of every export. You can switch to binary counting in the settings when you know the destination uses it.
Frequently asked questions
Why does Windows show a different size from my phone?+
Windows divides by 1,024 and labels the result KB; many phones and macOS divide by 1,000. The file is the same; only the unit differs.
Is 1 MB 1,000 KB?+
In decimal units, yes: 1,000,000 bytes. In binary units, 1 MiB is 1,048,576 bytes.
Written for the current Metro Research tools. Spot an error? See our quality and corrections policy.