TB vs GB Storage Confusion: Why Your Drive Looks Smaller
A "500 GB" drive shows ~465 GB because OSes use binary GiB. Decimal GB = 10⁹ bytes; binary GiB = 2³⁰. Exact factors and the calculator.
By The UnitFig Editorial Team · August 29, 2026 · reviewed against NIST and SI reference sources
Decimal vs binary
Drive makers use decimal: 1 GB = 1,000,000,000 bytes, 1 TB = 1,000,000,000,000 bytes. Operating systems count in binary: 1 GiB = 1,073,741,824 bytes. So a "500 GB" drive holds 500×10⁹ bytes = 465.66 GiB, which Windows labels "465 GB". The space is not missing — the units differ.
Mistake 1: expecting 1000 vs 1024
Treating GB as 1024 MB (binary) when the spec means 1000 MB (decimal) overstates capacity by ~7% at TB scale. Match the unit system to the context: marketing = decimal, RAM/OS = binary (GiB/MiB).
Mistake 2: mixing TB and GiB
Comparing a decimal TB spec to a binary GiB reading directly is apples-to-oranges. Convert within one system: 1 TB = 1000 GB (decimal) = 931 GiB (binary).
Frequently Asked Questions
Why does 500 GB show as 465?
Because Windows counts in binary GiB (2³⁰ bytes); 500×10⁹ bytes = 465.66 GiB, displayed as "465 GB".
Is GB 1000 or 1024 MB?
Decimal GB = 1000 MB (drive specs). Binary GiB = 1024 MiB (RAM/OS). They are different units.
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Quick Summary
The "missing" drive space is a decimal-vs-binary unit mismatch: 500 GB (decimal) = 465 GiB (binary). Use GiB/MiB for OS figures and GB/TB for specs; the calculator converts both ways exactly.
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Disclaimer
Unit conversions on this site use internationally recognized, fixed conversion factors (for example, 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 °F = (°C × 9/5) + 32). They are provided for general, informational, and educational use. For applications where accuracy is critical — such as medical dosing, engineering, scientific research, trade, or legal compliance — always verify results against authoritative sources such as the U.S. National Institute of Standards and Technology (NIST) and the official International System of Units (SI) brochure, and follow any applicable local standards.
Exact Constants & Authoritative Sources
Every conversion on this page uses the fixed, internationally agreed constants below — drawn from NIST and the SI Brochure. No values are estimated or rounded as if exact. See the full list on our Sources & Standards page.
- EXACT1 kibibyte (KiB) = 1024 bytes (exact, binary, IEC)
- EXACT1 kilobyte (kB, decimal) = 1000 bytes (exact, SI)
- EXACT1 mebibyte (MiB) = 1,048,576 bytes; 1 megabyte (MB) = 1,000,000 bytes
- EXACT1 gibibyte (GiB) = 1,073,741,824 bytes; 1 gigabyte (GB) = 1,000,000,000 bytes
Common Pitfalls & How to Avoid Them
GB vs. GiB (the "missing" storage space)
Operating systems label gibibytes as "GB". A "500 GB" drive holds 500 × 10⁹ bytes = 465.66 GiB, which Windows shows as ~465 GB. The space is not "lost" — decimal vs. binary units differ.
kB vs. KB capitalization
Strictly, kB = 1000 bytes (SI) and KB is sometimes used for 1024 (binary). To avoid ambiguity use KiB/MiB/GiB for binary and kB/MB/GB for decimal.
A unit-conversion reference site has no manufacturer-specific or device calibration parameters, so "layered tuning" does not apply here. The only real error-handling is input validation: the converter rejects non-numeric, empty, or out-of-range entries and shows a clear message, then falls back to exact constants above. No estimated or rounded figures are ever presented as exact.
Authoritative sources for this page
- IEC (International Electrotechnical Commission) — IEC 80000-13 — Quantities and units for information science and technology (binary prefixes)
Last Updated 2026 | This article was reviewed for accuracy