Storage Calculator
Why a "1 TB" Drive Never Shows 1,000 GB in Your OS
Storage capacity gets measured two different ways, and the mismatch between them is the reason a drive labeled 1 TB shows up as roughly 931 GB in Windows or macOS. Manufacturers count in decimal (1 TB = 1000 GB), following the same metric convention as everything else measured in kilo-, mega-, and giga-. Operating systems have historically counted in binary (1 "TB" = 1024 "GB"), because memory and storage addressing is inherently base-2. This calculator converts between bits, bytes, and the standard size units under either convention.
The Formula
Every conversion routes through bytes as the common unit, using the base you select:
result = bytes / base^(target unit exponent)
base = 1024 (binary/IEC convention) or 1000 (decimal/SI convention)
Bits convert separately: 1 byte = 8 bits, independent of which base is chosen for the byte-based units.
Where This Distinction Matters
- Buying storage — understanding why a "2 TB" drive reports less free space than expected avoids a support call that isn't actually a defect.
- Cloud billing — providers like AWS and Google Cloud bill storage in decimal GB/TB, while your OS may report usage in binary units, so the numbers on your invoice and your file browser won't match exactly.
- File transfer planning — converting a file size to bits is the first step in estimating download or upload time over a connection rated in Mbps.
- System specs — RAM is essentially always specified and addressed in binary units, since memory is physically organized in powers of two.
Binary vs. Decimal: The Same Label, Different Byte Counts
| Unit | Binary (1024-based) | Decimal (1000-based) |
|---|---|---|
| KB | 1,024 bytes | 1,000 bytes |
| MB | 1,048,576 bytes | 1,000,000 bytes |
| GB | 1,073,741,824 bytes | 1,000,000,000 bytes |
| TB | 1,099,511,627,776 bytes | 1,000,000,000,000 bytes |
The formal IEC names for binary units are KiB, MiB, GiB, and TiB, but KB, MB, GB, and TB remain the labels most operating systems and drive packaging actually display.
How to Use This Calculator
- Enter the Value you want to convert.
- Choose the From unit and the To unit, from bit up through petabyte.
- Select whether to use the Binary (1024-based) or Decimal (1000-based) standard.
- Select Calculate to see the converted value along with the intermediate byte figure.
Related Calculations
Estimating how long a file takes to move over a network? Use the Download Time Calculator. Sizing storage for a cloud subscription instead of local disks? See the Cloud Storage Calculator.