Convert between bits, bytes, kilobytes, megabytes, gigabytes, and terabytes, using either decimal (1000-based) or binary (1024-based) units.
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Digital storage units come in two competing counting systems that cause frequent confusion: the decimal system (where 1 kilobyte = 1,000 bytes, following the standard metric prefix meaning), and the binary system (where 1 kibibyte = 1,024 bytes, since computers naturally work in powers of two). Storage device manufacturers (hard drives, SSDs, USB drives) almost universally advertise capacity using the decimal system, since it produces larger, more marketable numbers, while most operating systems display file and drive sizes using the binary system — which is exactly why a drive advertised as "1TB" shows only about 931 GB of usable space when you check it in Windows or macOS. This calculator supports both counting bases so you can convert accurately regardless of which convention your specific comparison requires, whether you're checking a manufacturer's spec sheet or your operating system's own file browser. Understanding which convention a given number follows is the key to making sense of the discrepancy rather than assuming a device is somehow missing storage.
Few consumer tech frustrations are as consistently confusing, or as consistently misunderstood as intentional deception, as buying a storage device advertised with one capacity and then seeing a noticeably smaller number when actually checking it on a computer. The gap isn't a manufacturing shortfall or a marketing trick — it's the direct, mathematically consistent result of two different, both technically valid, ways of counting the same underlying bytes.
The decimal system defines 1 kilobyte as exactly 1,000 bytes, 1 megabyte as 1,000 kilobytes, and so on — following the same metric prefix convention used everywhere else in science and everyday measurement, where 'kilo' always means exactly one thousand. This is the system storage manufacturers use on product packaging and marketing materials, in part because it produces the larger of the two possible numbers for any given amount of actual physical storage.
The binary system instead defines 1 kibibyte (KiB) as 1,024 bytes — precisely 2¹⁰ — because computer memory and storage addressing naturally operates in powers of two at the hardware level. This binary convention is what most operating systems, including Windows and macOS, use internally when calculating and displaying file sizes and drive capacities, even though many operating systems label the resulting units 'KB', 'MB', and 'GB' rather than the more precise 'KiB', 'MiB', and 'GiB' terminology.
The practical consequence compounds with each unit step upward: a drive advertised as holding 1,000,000,000,000 bytes (1 decimal terabyte) contains 1,000,000,000,000 ÷ 1,099,511,627,776 of a binary tebibyte — approximately 0.9095, which is why that same physical drive displays as roughly 931 GB in a binary-counting operating system. The percentage gap between the two systems grows larger at each successive unit (kilobyte to megabyte to gigabyte to terabyte), which is why the discrepancy becomes more noticeable, in absolute terms, on larger modern drives than it was on the smaller drives of decades past.
The International Electrotechnical Commission formally addressed this ambiguity by defining distinct binary-prefix units — kibibyte, mebibyte, gibibyte, tebibyte (KiB, MiB, GiB, TiB) — specifically to be used only for the 1,024-based binary counting system, reserving KB, MB, GB, and TB exclusively for the 1,000-based decimal system. In practice, however, informal usage of 'KB', 'MB', and 'GB' to mean either system remains extremely common, which is exactly the ambiguity this converter's explicit base selector is designed to remove.
The manufacturer used the decimal definition (1TB = 1,000,000,000,000 bytes) while your operating system displays the binary definition (1 TiB = 1,099,511,627,776 bytes), making the same physical drive appear as roughly 931 GB in your OS.
Use binary (1024) to match what Windows File Explorer or macOS Finder shows you; use decimal (1000) to match what's printed on a storage device's packaging or a marketing spec sheet.
Yes — the International Electrotechnical Commission (IEC) defined "kibibyte," "mebibyte," and "gibibyte" (KiB, MiB, GiB) specifically for the binary (1024-based) units, though "KB," "MB," and "GB" are still very commonly used informally for both systems.