This is the one converter on this site where “1,000 versus 1,024” is the entire subject, not a footnote — two incompatible conventions both call themselves “KB”, and this calculator keeps them cleanly separate rather than pretending they are the same thing.
Key terms
- Decimal (SI) — 1 KB = 1000 bytes, 1 MB = 1,000,000 bytes, and so on. This is what SI actually defines “kilo” to mean, and it is how storage manufacturers label their products.
- Binary (IEC) — 1 KiB = 1024 bytes, 1 MiB = 1,048,576 bytes, and so on. This is how computer memory and most operating systems actually address and report storage.
Why your 1 TB drive shows up as 931 GB
Nothing is missing from the drive. The manufacturer labelled it using the decimal definition: 1 TB = 1,000,000,000,000 bytes, matching SI exactly. Your operating system’s “Properties” dialog reports the identical byte count using the binary definition — 1 TiB = 1,099,511,627,776 bytes — but very often still displays the label “GB” instead of the correct “GiB”. The same number of bytes is being described by two different rulers, and 1,000,000,000,000 bytes divided by 1,073,741,824 (one binary “gigabyte”) comes out to roughly 931 — which is exactly the number people see and assume means storage went missing.
How it works
Two separate systems
Decimal: 1 GB = 1000³ bytes exact · Binary: 1 GiB = 1024³ bytes exact
Switching the toggle does not convert a value from one system to the other — it changes which ruler every field is measured with, because 1 GB and 1 GiB are two different quantities, not two names for the same one.
How to use this calculator
- Pick Decimal (SI) if you are working with a manufacturer’s advertised capacity, or Binary (IEC) if you are working with what an operating system reports.
- Type a value into any field within that system.
- The rest update within the same system — switching the toggle starts a fresh conversion, it does not translate your number across.
Frequently asked questions
So is my hard drive lying to me?
No — the manufacturer’s “1 TB” is exactly one trillion bytes, precisely as advertised. Your computer is just reporting the same byte count on a different scale and, unhelpfully, often keeps calling that scale “GB” when it should say “GiB”.
Why does 1024 show up instead of a round 1000?
Because computer memory is addressed in binary, and 1024 (2¹⁰) is the power of two closest to 1000 — an old convenience that stuck as a naming convention long after it stopped being the only sensible choice.
What is the correct way to write “kibibyte”?
KiB, capital K, lowercase i, capital B — defined by the IEC specifically to remove the ambiguity that “KB” carries. It has not been widely adopted by consumer software, which is exactly why the ambiguity persists.
Does this affect internet speed measurements too?
Yes, in a related way — internet speeds are conventionally quoted in bits per second (decimal), while file sizes are quoted in bytes (sometimes decimal, sometimes binary), which is why a “100 Mbps” connection does not transfer a “100 MB” file in one second — there is an 8x factor between bits and bytes on top of the decimal/binary question.
