Data units

How many KB are in 1 MB?

Both answers are right. Which one applies depends on whether you are reading an operating system or a marketing box, and the gap compounds at every step.

1 MB is 1,024 KB in the binary system and 1,000 KB in the decimal system. Windows, macOS and Linux file managers use the binary value, so a file they call 1 MB is 1,048,576 bytes. Storage manufacturers, network operators and telecom bills use the decimal value, so a “1 MB” allowance is 1,000,000 bytes. The strictly correct name for the binary unit is the mebibyte (MiB), but almost nobody writes it that way.

Worked out 2026-09-10 (IST) · IEC binary prefixes vs SI decimal prefixes

Both systems, side by side

Data units in binary and decimal
Unit	Binary (what your OS shows)	Decimal (what vendors sell)	Difference
1 KB	1,024 bytes	1,000 bytes	2.4%
1 MB	1,048,576 bytes	1,000,000 bytes	4.9%
1 GB	1,073,741,824 bytes	1,000,000,000 bytes	7.4%
1 TB	1,099,511,627,776 bytes	1,000,000,000,000 bytes	10.0%
1 PB	1,125,899,906,842,624 bytes	1,000,000,000,000,000 bytes	12.6%

Advertised capacity against displayed capacity

What a drive says on the box, and what your operating system will report after you plug it in.

Drive capacity as sold and as shown
Sold as	Actual bytes	Windows shows	Apparent loss
128 GB	1,28,00,00,00,000	119.21 GB	6.9%
256 GB	2,56,00,00,00,000	238.42 GB	6.9%
512 GB	5,12,00,00,00,000	476.84 GB	6.9%
1 TB	10,00,00,00,00,000	0.91 TB	9.1%
2 TB	20,00,00,00,00,000	1.82 TB	9.1%
4 TB	40,00,00,00,00,000	3.64 TB	9.1%

The rule of thumb. Anything you buy is decimal. Anything you read on screen is binary. Multiply a decimal figure by 0.931 to predict what Windows will show for a drive, or by 0.953 for a single megabyte-sized file.

The formula

binary: 1 KiB = 2¹⁰ = 1,024 bytes; 1 MiB = 2²⁰; 1 GiB = 2³⁰

decimal: 1 kB = 10³ = 1,000 bytes; 1 MB = 10⁶; 1 GB = 10⁹

convert: decimal GB × 0.9313 = binary GiB

Check your own numbers

Convert between bytes, KB, MB, GB and TB in either system, and see both answers side by side.

Data Storage ConverterBytes to KB, MB, GB, TB and PB, in binary and decimal.

Frequently asked

Why does my 1 TB hard drive show as 931 GB?

Because the manufacturer sold you 1,000,000,000,000 decimal bytes and Windows divides by 1,024 three times to display it. 1,000,000,000,000 / 1024 / 1024 / 1024 = 931.32. No storage is missing; the two numbers are the same quantity of bytes described in different bases. The discrepancy is 7.4 per cent at the terabyte level and grows with every step up.

Is KB or kB correct?

Strictly, kB with a lowercase k is the SI decimal kilobyte (1,000 bytes) and KiB is the binary kibibyte (1,024 bytes). In everyday writing KB is used for both and the context decides. If a document needs to be unambiguous - a storage contract, a technical spec - use KiB / MiB / GiB for binary and kB / MB / GB for decimal.

How many KB is a typical photo?

A photo from a modern phone camera is usually 2 to 6 MB, which is roughly 2,000 to 6,000 KB decimal. A compressed web image is typically 100 to 300 KB, and an icon or thumbnail 5 to 50 KB. A page of plain text is about 2 KB. These are the numbers to use when estimating whether something will fit in an email attachment limit, which is usually 25 MB.

Does my mobile data plan use 1000 or 1024?

Indian telecom operators bill in decimal, so a 1.5 GB daily pack is 1,500 MB = 1,500,000 KB. Your phone, however, counts the data it has used in binary, which is why the operator app and the phone settings can disagree by a few per cent on the same day. The operator figure is the one that decides when your pack runs out.

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