Data Storage Converter
Convert between bytes, KB, MB, GB, TB and more.
Why Your 1 TB Drive Shows as 931 GB — The Decimal vs. Binary Divide
This is one of the most common technical complaints in computing: you buy a 1 TB drive, plug it in, and Windows reports roughly 931 GB of capacity. The drive manufacturer is not cheating you — both numbers are factually correct, but they measure the same thing in different units, and the industry has refused to standardize for decades.
Hard drive manufacturers use SI (decimal) prefixes: 1 TB = 1012 bytes = 1,000,000,000,000 bytes. Windows and most operating systems report storage in binary, where 1 TB historically meant 240 bytes = 1,099,511,627,776 bytes. Divide the actual byte count (1012) by the binary TB (240) and you get 0.9095 — hence "931 GB" on a 1 TB drive. The discrepancy grows with drive size: a 4 TB drive appears as ~3.64 TB, a 10 TB drive as ~9.09 TB.
The IEC Prefixes — The Fix Nobody Adopted
In 1998, the International Electrotechnical Commission introduced unambiguous binary prefixes to solve this: kibibyte (KiB = 210 = 1,024 bytes), mebibyte (MiB = 220 = 1,048,576 bytes), gibibyte (GiB = 230), tebibyte (TiB = 240). The IEC standard is technically correct and unambiguous. In practice, it is barely used outside Linux disk utilities and technical specifications — most tools, vendors, and even standards documents still mix decimal and binary usage of KB/MB/GB.
The practical rule: assume storage capacity (drives, SSDs, flash) uses decimal GB/TB; assume operating system reports, RAM, and file sizes use binary GiB/TiB even when labeled GB/TB.
Network Bandwidth: The Bit vs. Byte Trap
Internet service providers advertise bandwidth in bits per second (Mbps, Gbps), while download speeds in browsers and apps display in bytes per second (MB/s). This is not a conspiracy — bits per second is the correct unit for transmission capacity, and bytes per second is correct for data volume. The relationship is 8 bits per byte, so a 100 Mbps connection delivers a maximum of 12.5 MB/s of actual file data (minus protocol overhead, which in practice reduces it to 10–11 MB/s). Knowing this saves you from calling your ISP to complain about a "slow" connection that is actually running at rated capacity.
Practical Reference Points
- 1 byte: a single ASCII character.
- 1 KB (1,000 bytes): a short plain-text email.
- 1 MB: about 1 minute of compressed voice audio (MP3 at 128 kbps).
- 1 GB: roughly 250 uncompressed 12-megapixel photos in JPEG, or about 1 minute of 4K video.
- 1 TB: approximately 250 hours of 1080p video at typical streaming bitrates.
How to Use This Tool
- Enter a value in any unit — bits, bytes, KB, MB, GB, TB, PB, or their KiB/MiB/GiB/TiB binary equivalents.
- All other units update instantly with exact values.
- Both decimal and binary families are displayed side-by-side so you can see the difference clearly.
⇄ FAQ
01 Why does 1 GB equal 1,073,741,824 bytes in some contexts and 1,000,000,000 in others? +
Two competing standards: SI decimal (1 GB = 10^9 bytes, used by storage manufacturers) and binary (1 GiB = 2^30 = 1,073,741,824 bytes, historically used by operating systems and often mislabeled as GB). The 7.4% difference between them accumulates at larger scales — 1 TiB is about 9.9% larger than 1 TB.
02 How do I convert Mbps to MB/s for download speeds? +
Divide by 8. A 100 Mbps connection can theoretically deliver 12.5 MB/s. In practice, TCP/IP overhead and protocol headers reduce this by 5–10%, so expect 10–11 MB/s on a 100 Mbps link.
03 Why do some utilities report drive size in GiB but label it GB? +
Most utilities use the binary calculation but the decimal label out of long-established habit. macOS switched to reporting true decimal GB in OS X 10.6 (Snow Leopard, 2009), which is why Mac users suddenly saw their drives "gain" capacity after the update — the bytes were always there, just reported in a different unit.
04 What is the largest standard data unit? +
In SI decimal, the defined prefixes go up to yottabyte (YB = 10^24 bytes). In IEC binary, yobibyte (YiB = 2^80). The total amount of data stored worldwide in 2024 is estimated at around 120 zettabytes — the scale makes petabytes and exabytes the practical working units for cloud and data center contexts.
