Kilobytes to Megabytes Converter

The short answer: 1,000 KB in a megabyte

On the decimal scale used by drive makers, phone makers and the International System of Units, one megabyte is 1,000 kilobytes. So 500 KB is 0.5 MB, 2,000 KB is 2 MB, and 10,000 KB is 10 MB. Divide by 1,000 and you are done.

That is the whole conversion in one line. The trouble starts because Windows, and a lot of older software, divides by 1,024 instead. A 500 KB file holds 500,000 bytes, which is 0.477 MiB, and Windows labels that same file as 488 KB because it counts 1,024 bytes to a kilobyte. Both answers describe the same file. They just use different definitions of the same word.

The decimal definition is the official one. NIST's table of SI prefixes sets kilo at 10 to the third power, which is 1,000, and mega at 10 to the sixth, which is 1,000,000. A kilobyte is 1,000 bytes and a megabyte is 1,000,000 bytes, by the book.

So why does your computer disagree? Because early operating systems counted in powers of two, which is natural for memory addressed in binary, and the habit stuck. The names stayed the same while the arithmetic changed underneath them, and that is the source of nearly every confusing file size you have seen.

Where 1,024 comes from

1,024 is 2 to the tenth power. Computer memory is organized in powers of two, so a block of 1,024 bytes is a natural unit to a programmer in a way that 1,000 bytes is not. Early documentation used KB for 1,024 bytes because that is what the hardware delivered.

In 1998 the International Electrotechnical Commission created separate names for the binary units to end the confusion. A kibibyte is 1,024 bytes, a mebibyte is 1,024 kibibytes, and a gibibyte is 1,024 mebibytes. The IEC page on binary prefixes explains the reasoning, and NIST keeps a reference page on the binary prefixes as well.

The new names never caught on with the public. Windows still labels binary sizes as KB, MB and GB. Drive makers label decimal sizes with the same three letters. Both are technically wrong under the strict standard, since KB should mean 1,000 bytes and KiB should mean 1,024, but the labels are what ship, so the gap survives.

One consequence is worth remembering: the gap grows with each step up. It is 2.4% at the kilobyte level, 4.9% at the megabyte level, 7.4% at the gigabyte level, and 10% at the terabyte level. That compounding is why the discrepancy on a hard drive is much bigger than the discrepancy on a text file.

KB to MB conversion table

This table gives both answers for common sizes. The decimal column is what a manufacturer means. The binary column is what Windows shows when it labels the same number MB.

The gap is always the same 4.6% at this level, because 1,000,000 / 1,048,576 = 0.9537. Multiply any decimal answer by 0.9537 to get the binary one: 4 MB becomes 3.81 MiB, and 10 MB becomes 9.54 MiB. The anchor worth remembering is that 1 MiB is 1,048.576 KB, so a 1,000 KB file is just under one mebibyte.

Why a 1 TB drive shows 931 GB

A drive sold as 1 TB holds 1,000,000,000,000 bytes. That is 1,000 GB on the decimal scale, which is what the box says and what the manufacturer is entitled to print. Windows divides that same byte count by 1,024 three times, and gets 931.3 GiB, which it labels as 931 GB.

Nothing is missing. The drive holds exactly what was advertised. The number on screen is smaller because it is measured with a bigger unit. Divide 1,000,000,000,000 by 1,024 and you get 976,562,500 KiB, divide again for 953,674 MiB, and divide once more for 931.3 GiB.

The same math explains a 128 GB phone that reports 119 GB of storage, and a 512 GB laptop that shows 476 GB. The percentage gap is the same 7.4% at the gigabyte level every time. Once you know the pattern, the numbers stop looking like a scam.

Some of the reported gap is also the operating system itself, which occupies several gigabytes before you install anything. On a 128 GB phone, expect 10 to 15 GB for the system and preinstalled apps on top of the unit conversion, so 119 GB of visible space is normal rather than generous.

Network speeds use decimal too

Internet speed is measured in megabits per second, and that is always decimal. A 100 Mbps connection moves 100,000,000 bits per second, not 104,857,600. There is no binary megabit in common use, so network numbers do not have the same ambiguity as storage numbers.

The conversion that trips people up is bits to bytes. There are 8 bits in a byte, so a 100 Mbps connection downloads at 100 / 8 = 12.5 MB per second at best. A 1 Gbps connection tops out at 125 MB per second.

Those times assume the file is 1 GB decimal, which is 1,000 MB, and that the connection runs at full speed. Real downloads run below the plan speed because of server limits, Wi-Fi and congestion, so add 20% to 30% to every number in the last column.

Reading file sizes in email, photos and documents

Most people meet the KB and MB distinction at an attachment limit. A typical email account caps attachments at 25 MB, which is 25,000 KB on the decimal scale, or 23.8 MiB if your mail client counts in binary. Either way, a folder of photos that totals 30,000 KB will not send.

Rough sizes for planning, all decimal:

• A page of text is about 2 KB, so a 100 page document is around 200 KB.
• A phone photo runs 3 to 6 MB, or 3,000 to 6,000 KB.
• A song at 256 kbps is about 8 MB, so 1,000 KB is roughly an eighth of a song.
• A minute of 1080p video is about 130 MB, which is 130,000 KB.
• A PDF with images lands between 1 and 10 MB depending on how the images were compressed.

This is where the 2.4% gap at the kilobyte level becomes invisible. Nobody cares whether a photo is 4,000 KB or 3,906 KiB, because the difference is 94 KB and the upload succeeds either way. The gap only starts to matter at the gigabyte level, where it is measured in tens of gigabytes.

KiB and MiB: when the binary names matter

If you write documentation, ship software, or argue with a hosting provider about disk quotas, the binary names are worth using precisely. KiB, MiB, GiB and TiB remove the ambiguity that KB, MB and GB carry.

The rule is simple. A decimal unit steps by 1,000 and a binary unit steps by 1,024. One MiB is 1,024 KiB, one GiB is 1,024 MiB, and one TiB is 1,024 GiB. Mixing the two in one sentence is how a 1 TB drive becomes "931 GB" in a support ticket.

Most consumer software still uses the short names for binary sizes, and that is unlikely to change because the labels are baked into decades of interfaces. The practical approach is to state the base when the number matters. "500 MB (decimal)" and "500 MiB" are both unambiguous, and either one beats a bare MB that could mean 500,000,000 or 524,288,000 bytes.

For everyday use, the difference is small enough to ignore below 100 MB and large enough to notice above 100 GB. That is the whole rule of thumb.

Checking a conversion by hand

You do not need a calculator for most of these. Three mental moves cover the common cases.

• KB to MB, decimal: move the decimal point three places left. 500 KB becomes 0.5 MB, and 12,500 KB becomes 12.5 MB.
• KB to MiB, binary: take 4.6% off the decimal answer. 500 KB is 0.5 MB, and 0.5 x 0.9537 = 0.477 MiB.
• MB to KB: multiply by 1,000 on the decimal scale, or by 1,024 on the binary one. 4 MB is 4,000 KB, and 4 MiB is 4,096 KiB.

The percentage changes with each step up because the gap compounds. One KB and one KiB differ by 2.4%, one MB and one MiB by 4.9%, one GB and one GiB by 7.4%, and one TB and one TiB by 10%. Each step multiplies the last gap by 1.024 again, which is why the numbers drift apart faster than people expect.

If you need the exact figure, use the converter at the top of the page and pick the unit that matches the label on the file. Choosing KB (1,000) when the source meant KiB (1,024) is the one input error that throws the answer off by more than a rounding step.

Conversions use the SI decimal factors and the IEC binary factors. Both results are shown so you can match whichever number your software displays.