How data storage units work
Digital storage is measured in bytes, and each bigger unit is a fixed multiple of the last. The catch is that there are two conventions: binary (each step ×1024) and decimal (each step ×1000). This converter lets you pick either, so your answer matches what you're comparing against.
Binary vs decimal — why the mismatch?
Computers work in powers of two, so operating systems count 1 KB = 1024 bytes. Storage manufacturers, however, sell drives using the decimal meaning, 1 KB = 1000 bytes. The gap grows at each level, which is why a drive sold as "1 TB" (1,000,000,000,000 bytes) shows up as roughly 931 GB in Windows. Neither is "wrong" — they're just different definitions.
Advertised vs actual storage capacity
Drive and phone makers count in decimal (1 GB = 1,000,000,000 bytes); Windows and most apps count in binary (1 GB = 1,073,741,824 bytes). Nothing is missing — it's the same number of bytes in a smaller-looking unit. The gap grows with each step up: about 7% at GB, 9% at TB.
| Advertised | Shown on your computer | Apparent shortfall |
|---|---|---|
| 32 GB | 29.8 GB | 6.9% |
| 64 GB | 59.6 GB | 6.9% |
| 128 GB | 119.2 GB | 6.9% |
| 256 GB | 238.4 GB | 6.9% |
| 500 GB | 465.7 GB | 6.9% |
| 512 GB | 476.8 GB | 6.9% |
| 1 TB | 0.91 TB (931 GB) | 9.1% |
| 2 TB | 1.82 TB (1,863 GB) | 9.1% |
| 4 TB | 3.64 TB (3,725 GB) | 9.1% |
| 8 TB | 7.28 TB (7,451 GB) | 9.1% |
| 16 TB | 14.55 TB (14,901 GB) | 9.1% |
Formatted drives also lose a little more to the file system and any recovery partition, so the free space you see can be slightly lower still. macOS and iOS count in decimal, so they show the advertised figure.
The units, largest to smallest
- 1 TB = 1024 GB
- 1 GB = 1024 MB
- 1 MB = 1024 KB
- 1 KB = 1024 bytes
Why does my 1 TB drive only show 931 GB?
Because 1 TB as sold is 1,000,000,000,000 bytes, and Windows divides by 1,024 three times instead of 1,000: 1012 ÷ 1,073,741,824 = 931.32 GB. No storage is missing — it's two different definitions of a gigabyte.
How much space is actually on a 256 GB phone or SSD?
About 238.4 GB in binary units, before the operating system and pre-installed apps take their share.
How many MB in a GB?
In the binary system used by operating systems, 1 GB = 1024 MB. In the decimal system used by drive makers, 1 GB = 1000 MB. Pick the base above to match your source.
How many GB in a TB?
1 TB = 1024 GB (binary) or 1000 GB (decimal). So a "2 TB" drive holds about 2048 GB by the binary count, but is often shown as roughly 1862 GB in your OS.
Why does my hard drive show less space than advertised?
Because the manufacturer measured in decimal (1 GB = 1,000,000,000 bytes) but your operating system reports in binary (1 GB = 1,073,741,824 bytes). The data is all there — it's just counted differently, so a "1 TB" drive reads as about 931 GB.
How many KB in a MB?
1 MB = 1024 KB in binary, or 1000 KB in decimal. A KB (kilobyte) is 1024 bytes in the binary convention.
What is a byte?
A byte is 8 bits and can store a single character of text. Everything larger — KB, MB, GB, TB — is just a multiple of bytes.