File Size Converter
Convert bytes, KB, MB, GB and TB — in both the decimal and binary systems, side by side.
Decimal (SI) — 1 KB = 1,000 bytes
Used by storage manufacturers, networks and macOS
Binary (IEC) — 1 KiB = 1,024 bytes
Used by Windows, RAM sizing and most operating systems
Why your 1 TB drive shows as 931 GB: the manufacturer counts 1 TB as 1,000,000,000,000 bytes (decimal), but Windows displays it using 1024-based units and labels them “GB”. The same bytes, two counting systems — nothing is missing.
About this tool
Converting file sizes should be simple arithmetic, and it would be if the world agreed on what a kilobyte is. It doesn't: storage manufacturers, networks and macOS count 1 KB as 1,000 bytes (the decimal or SI system), while Windows, RAM sizing and most operating systems count 1,024 bytes and still call it "KB" (properly a kibibyte, KiB). Most converters silently pick one and hide the ambiguity. This one shows **both systems side by side**, so you always know which number you're looking at.
Enter a size in any unit — decimal (KB, MB, GB, TB, PB) or binary (KiB, MiB, GiB, TiB, PiB) — and every other unit in both systems is calculated at once. The difference compounds as sizes grow: it's only 2.4% at the kilobyte level but nearly 10% by the terabyte, which is exactly why the numbers stop matching on large drives.
That mismatch is the question this tool really answers: **why does a 1 TB drive show as 931 GB?** The manufacturer sold you 1,000,000,000,000 bytes, and Windows divided by 1024 three times and labelled the result "GB". Nothing is missing and nothing is faulty — it's two counting systems wearing similar labels. Everything computes instantly in your browser.
How to use the File Size Converter
- 1Enter a size and choose its unit — decimal (KB, MB, GB) or binary (KiB, MiB, GiB).
- 2Every other unit is calculated in both systems at once.
- 3Compare the two columns to see how much the systems diverge at your size.
- 4Use decimal for storage marketing and networks; binary for what Windows reports.
Frequently asked questions
Why does my 1 TB hard drive show as 931 GB?
The manufacturer defines 1 TB as 1,000,000,000,000 bytes (decimal). Windows divides that by 1024 three times to reach 'GB' — giving 931. Same bytes, different counting system. No space is missing; the labels just disagree, which this converter makes visible.
What's the difference between MB and MiB?
1 MB (megabyte, decimal) is 1,000,000 bytes; 1 MiB (mebibyte, binary) is 1,048,576 bytes — about 4.9% more. The IEC introduced the -bi- names (KiB, MiB, GiB) specifically to end this ambiguity, though everyday usage still mostly says 'MB' for both.
How many MB are in a GB?
1,000 MB in decimal (the system storage manufacturers and macOS use), or 1,024 MiB in binary (what Windows reports). Both answers are correct within their own system — which is exactly why this converter shows them together rather than picking one.
Which system should I use?
Match your context: decimal for storage capacity, network speeds, macOS and marketing figures; binary for what Windows displays, RAM sizes and most low-level computing. When precision matters, state the unit explicitly — 'GiB' removes all doubt.
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