💾 Data Storage and Transfer Guide
Complete data measurement guide — why your 1 TB drive shows 931 GB, Mbps to MB/s conversion, decimal vs binary prefixes, and bandwidth planning.
Data has two overlapping unit systems, and mixing them causes confusion every day. Your new 2 TB SSD shows 1.86 TB in Windows. Your 100 Mbps internet downloads at 11.92 MiB/s.
The root cause: decimal vs binary
SI uses base-10 (kilo- = x1,000). Computers use base-2 (binary = x1,024). The IEC standardized new names in 1998: KiB, MiB, GiB, TiB. Microsoft still labels binary values with decimal names in Explorer.
How big is the difference?
At GB level: 7.4% gap. A 1 TB drive = 1 trillion bytes = 931 GiB = "931 GB" in Windows. At PB level: 14.9% — huge in enterprise storage.
Transfer rates
Bandwidth is in bits. File sizes are in bytes. Always divide by 8.
- 25 Mbps = 3.125 MB/s — one 4K stream
- 100 Mbps = 12.5 MB/s — standard household
- 1 Gbps = 125 MB/s — a 50 GB game downloads in 6.7 minutes
Related converters
Frequently asked questions
Why is my 1 TB drive only 931 GB?
Drives use decimal GB (1 TB = 1 trillion bytes). Windows uses binary GiB but labels it GB. 1 trillion / 1.07 billion = 931 GiB.
How many bits in a byte?
8 bits = 1 byte. Transfer speeds are in bits (bps, Mbps) while file sizes are in bytes.
Is 100 Mbps the same as 100 MB/s?
No! 100 Mbps = 12.5 MB/s (decimal) = 11.92 MiB/s (binary). Always divide by 8.
Difference between MB and MiB?
MB (decimal) = 1M bytes. MiB (binary) = 1,048,576 bytes. The i prefix was adopted in 1998.
Last updated — conversions use exact ISO unit definitions.