Why does my new hard drive show less space than advertised?

This is the decimal-vs-binary mismatch, not missing storage -- manufacturers advertise capacity in decimal (1 TB = 1,000,000,000,000 bytes, the SI-correct meaning), but Windows and most operating systems report free space in binary units while mislabeling them with decimal unit names (showing "GB" when it actually means GiB). The bytes are genuinely all there; only the unit label is ambiguous.

Which mode should I use to check if a file fits on a drive?

Match whatever your operating system is showing -- if your OS reports drive space in the units it calls "GB" but is really computing in binary (as Windows does), use binary mode here for an apples-to-apples comparison; if you're working from a manufacturer's advertised decimal capacity, use decimal mode.

Are KiB, MiB, and GiB the "correct" names for binary units?

Yes -- KiB/MiB/GiB (kibibyte, mebibyte, gibibyte) are the internationally standardized names for binary (1024-based) units, introduced specifically to remove the ambiguity of using "KB/MB/GB" for both meanings. Most consumer software still labels binary values as "KB/MB/GB" out of habit, which is the root of most storage-size confusion.

Why do bits and bytes both appear at the top of the list?

They're the base units everything else derives from -- 8 bits make 1 byte, and this ratio holds regardless of whether you're working in decimal or binary mode, so bits and bytes anchor the rest of the unit ladder in both systems.

File Size / Data Storage Converter

Enter a value and unit — see it converted to every other size unit live, in either decimal (1000) or binary (1024) units.

How File Size / Data Storage Converter Works

Data storage has two competing definitions of "kilo," "mega," and "giga" -- decimal (powers of 1000, the way SI prefixes normally work) and binary (powers of 1024, the way computer memory is actually addressed). This mismatch is why a drive labeled "1 TB" shows up as roughly 931 GB in your operating system, and this converter lets you work in either system, or move between them, without the confusion.

Formula & Method

In decimal mode, each unit is 1000× the one before it (1 KB = 1000 bytes, 1 MB = 1,000,000 bytes, and so on) -- this is how storage manufacturers label drive capacity, and it matches the standard SI meaning of kilo/mega/giga. In binary mode, each unit is 1024× the one before it (1 KiB = 1024 bytes, 1 MiB = 1,048,576 bytes) -- this is how operating systems and RAM actually report size, since memory addressing is inherently base-2. Bits convert to bytes at a fixed 8 bits per byte in both modes, since that ratio doesn't depend on the decimal/binary choice.

Worked Example

A value of 1 in decimal GB mode equals 1,000,000,000 bytes (8,000,000,000 bits). That same byte count, viewed in binary mode, is only about 0.931 GiB -- which is exactly why a "1 TB" hard drive (1,000,000,000,000 bytes, the manufacturer's decimal definition) shows up as approximately 931 GiB in Windows' File Explorer, which reports binary units but labels them "GB."

Frequently Asked Questions

Why does my new hard drive show less space than advertised?: This is the decimal-vs-binary mismatch, not missing storage -- manufacturers advertise capacity in decimal (1 TB = 1,000,000,000,000 bytes, the SI-correct meaning), but Windows and most operating systems report free space in binary units while mislabeling them with decimal unit names (showing "GB" when it actually means GiB). The bytes are genuinely all there; only the unit label is ambiguous.
Which mode should I use to check if a file fits on a drive?: Match whatever your operating system is showing -- if your OS reports drive space in the units it calls "GB" but is really computing in binary (as Windows does), use binary mode here for an apples-to-apples comparison; if you're working from a manufacturer's advertised decimal capacity, use decimal mode.
Are KiB, MiB, and GiB the "correct" names for binary units?: Yes -- KiB/MiB/GiB (kibibyte, mebibyte, gibibyte) are the internationally standardized names for binary (1024-based) units, introduced specifically to remove the ambiguity of using "KB/MB/GB" for both meanings. Most consumer software still labels binary values as "KB/MB/GB" out of habit, which is the root of most storage-size confusion.
Why do bits and bytes both appear at the top of the list?: They're the base units everything else derives from -- 8 bits make 1 byte, and this ratio holds regardless of whether you're working in decimal or binary mode, so bits and bytes anchor the rest of the unit ladder in both systems.

Value

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