MB to KB: how many KB are in 1 MB?

How many KB are in 1 MB: 1,000 or 1,024?

Both answers are in use. In the decimal system that the SI units are based on, 1 MB is 1,000 KB, and 1 KB is 1,000 bytes. In the older binary system that Windows still uses to show file sizes, 1 MB is 1,024 KB, and 1 KB is 1,024 bytes.

Decimal: KB = MB × 1,000

Binary: KB = MB × 1,024

To end the confusion, the IEC introduced separate names for the binary units in 1998: a kibibyte (KiB) is 1,024 bytes and a mebibyte (MiB) is 1,048,576 bytes. NIST, the US standards body, recommends them. In practice most software still writes KB and MB for both, so you have to know which one a number means.

MB to KB conversion chart

The gap is 2.4% at the MB level. It grows with each step up: a gigabyte differs by about 7% and a terabyte by about 10%, which is why a new 1 TB drive shows as around 931 GB in Windows.

KB to MB

Go the other way by dividing:

MB = KB ÷ 1,000 (decimal) or KB ÷ 1,024 (binary)

Bytes, KB, MB and GB in one table

Each step up is 1,000 times bigger in decimal units, or 1,024 times in binary ones:

To go down a step, multiply; to go up, divide. 2.5 GB is 2,500 MB in decimal and 2,560 MB in binary; 750 MB is 0.75 GB or 0.73 GB.

To give a feel for the sizes:

• A page of plain text is a few KB.
• A signature scan for an exam form is usually asked to be 10 to 20 KB.
• A photo straight from a phone camera is usually a few MB.
• A minute of phone video runs to tens or hundreds of MB, depending on the resolution.

That spread is why a 3 MB phone photo has to shrink by more than 99% to meet a 20 KB limit, and why it needs fewer pixels as well as stronger compression to get there.

Which one your phone or computer uses

• Windows File Explorer counts in 1,024s. Seagate, the drive maker, explains that this is why drives look smaller in Windows than on the box: the box counts in 1,000s.
• Mac and iPhone count in 1,000s. Apple says only older systems, iOS 10 and earlier and OS X Leopard and earlier, reported sizes in binary.
• Android varies by phone maker and app, so check the exact number of bytes when it matters.

The same file can therefore show as 195 KB on a Windows PC and 200 KB on a Mac. Neither is wrong. The exact size in bytes is the one number every system agrees on, and both show it: right-click the file and choose Properties on Windows, or select it and choose Get Info on a Mac.

How to check a file’s exact size

• Windows: right-click the file, choose Properties, and read “Size”, which shows KB or MB and the exact bytes in brackets.
• Mac: select the file and press Command-I for Get Info. The size line shows the bytes too.
• iPhone and iPad: in the Files app, touch and hold the file, then choose Get Info.
• Android: in your file manager, open the file’s details or info. The wording differs between phone makers.

Our compress tools show the size of the result before you download it, so you can see straight away whether it fits the limit.

Upload limits on application forms

Forms rarely say which kind of KB they mean, and the check runs on the website’s server, not your computer. Two habits avoid rejections:

• Aim for the smaller reading. A file under 50,000 bytes is under 50 KB whichever way the site counts. If the limit is 50 KB, a target of 48 KB leaves room.
• Watch the minimum too. Many exam forms set a range, such as 10 KB to 20 KB for a signature. A file that’s too small is rejected as well, so don’t compress far past the lower end.

The signature size guide lists the exact KB ranges from SSC, IBPS and PAN notices.

Getting a file from MB down to KB

Converting the units doesn’t change a file. To turn a 3 MB phone photo into a 100 KB upload, the file itself has to get smaller:

A 12-megapixel photo has around 4,000 × 3,000 pixels; most forms want far fewer. Making it smaller in pixels first is what lets it reach a low KB target without turning blocky. The guide to reducing image size in KB shows what each size looks like.

MB and Mb are different units

A capital B means bytes and a small b means bits. There are 8 bits in a byte, so internet speeds in megabits per second (Mbps) need dividing by 8 to get megabytes per second.

A 100 Mbps connection moves at most 100 ÷ 8 = 12.5 MB a second

Kb, kB and KB also turn up for the same thing. In file sizes, treat all of them as kilobytes unless the context is network speed.

Sources

• NIST: Prefixes for binary multiples. KiB and MiB, adopted by the IEC in December 1998; 1 MB = 1,000,000 bytes, 1 MiB = 1,048,576 bytes
• Apple: How storage capacity is measured on Apple devices. Decimal on the packaging; binary only in iOS 10 and earlier and OS X Leopard and earlier
• Seagate: Why does my hard drive report less capacity than indicated on the drive’s label?. Drives are labelled in decimal; Windows reports in binary