Data Storage Converter

Binary vs Decimal Prefixes

Two competing prefix systems exist for data storage, and they produce different numbers for the same physical capacity. The SI (decimal) system uses powers of 1000: 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes. The IEC binary system uses powers of 1024: 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, 1 GiB = 1,073,741,824 bytes.

Why Your Hard Drive Looks Smaller Than Advertised

Hard drive and SSD manufacturers label their products using decimal (SI) prefixes because the numbers appear larger and are technically correct under SI definitions. A drive marketed as 500 GB contains exactly 500,000,000,000 bytes. However, Windows reports capacity in binary gibibytes: 500,000,000,000 ÷ 1,073,741,824 ≈ 465.7 GiB, which Windows displays as "465 GB". The discrepancy is not a defect — it is a labeling convention difference. macOS switched to decimal reporting in 2009, so it displays the same drive as 500 GB, matching the box.

Complete Prefix Table

The IEC 80000-13 standard defines binary prefixes with the suffix "-bi" and the symbol ending in "i" to distinguish them from SI prefixes:

Throughput vs Capacity

Storage capacity (how much data fits) is distinct from throughput (how fast data moves). A modern NVMe SSD may hold 2 TB while sustaining sequential read speeds of 7,000 MB/s. A SATA SSD of the same capacity tops out around 550 MB/s due to the SATA interface bandwidth limit. Throughput is almost always expressed in decimal megabytes per second (MB/s) or gigabits per second (Gb/s), not in binary units — so 1 Gb/s = 1,000,000,000 bits per second, not 1,073,741,824.

Worked Examples

Example 1 — The "missing" 35 GB on a 500 GB SSD. A 500 GB drive holds 500 × 10⁹ = 500,000,000,000 bytes. Windows divides by 1,073,741,824 (1 GiB) and reports 465.66 GB. The drive is fine — Windows is labelling GiB as "GB" without the "i". The user is not missing 35 GB; the units are just different.

Example 2 — Downloading a 50 GiB game on a 100 Mbps connection. 50 GiB = 50 × 1,073,741,824 × 8 bits ≈ 4.295 × 10¹¹ bits. At 100 Mbps = 10⁸ bits/s, the theoretical minimum is 4 295 seconds ≈ 71.6 minutes. Real-world overhead (TCP, throttling) typically adds 10–20%.

Example 3 — Sizing backup tape for 4 TB of data. An LTO-9 cartridge advertises 18 TB native capacity (decimal TB). 4 TB of source data = 4 × 10¹² bytes, well within one tape. But if your backup software reports capacity in TiB, 18 TB = 16.37 TiB — the "smaller" figure is the same tape measured differently.

Example 4 — Reading RAM specs. A stick labelled "16 GB DDR5" actually holds 16 × 2³⁰ = 17 179 869 184 bytes — because RAM addressing is binary by hardware design. The industry keeps the decimal-looking label "GB" even though every chip is binary. Always treat RAM as GiB internally even when the marketing says GB.

Common Pitfalls

• Assuming 1 GB = 1,073,741,824 bytes everywhere. True for Windows capacity display and RAM; false for hard drives, SSDs, and network speeds.
• Confusing bits and bytes. Network speeds use bits (Mbps); file sizes use bytes (MB). A 100 Mbps connection transfers ~12.5 MB/s, not 100 MB/s.
• Forgetting overhead. Filesystem metadata, block-alignment padding, and reserved blocks can consume 2–10% of advertised capacity on format.
• Mixing SI and IEC in the same calculation. A spreadsheet that multiplies a decimal TB figure by 1 024 to get GB will be systematically wrong.
• Thinking 1 Gbit = 1 GB. One is 10⁹ bits, the other is 10⁹ bytes (or 2³⁰ bytes). They differ by roughly 8×.

Frequently Asked Questions

Why did KiB/MiB/GiB exist if everyone just says "KB"? Before IEC introduced the "-bi" prefixes in 1998, "KB" meant both 1 000 bytes (drive makers) and 1 024 bytes (OS vendors), causing lawsuits. The binary prefixes exist specifically to disambiguate. Linux adopted them widely; Windows did not.

Does Windows 11 finally use decimal like macOS? No. As of 2026, File Explorer still labels binary gibibytes as "GB" in capacity displays. Third-party tools like PowerShell's Get-Volume report the same way.

Are internet speeds decimal or binary? Always decimal. 1 Gbps = 1 000 000 000 bits per second. ISPs, Ethernet standards, and Wi-Fi specs all use SI prefixes.

Why is a 1 TB SSD usable capacity around 931 GB? 1 TB = 10¹² bytes = 931.32 GiB, which your OS renders as 931 GB. No storage is missing — just two unit systems collide on screen.

Is a "10 Gig" network 10 GB/s? No. 10 GbE means 10 gigabits per second ≈ 1.25 GB/s. Real-world throughput after TCP overhead lands closer to 1.15 GB/s.

Related Calculators

For unit conversions across other physical quantities, try the Length Converter, Temperature Converter, and Weight Converter. Working with text encodings? The Base64 Encoder/Decoder shows how bytes inflate by 4:3 when base64-encoded. For number system conversions, see the Number System Converter.

Disclaimer

This calculator is provided for educational and informational purposes only. While we strive for accuracy, users should verify all calculations independently. We are not responsible for any errors, omissions, or damages arising from the use of this calculator.