Quick Values
Scale
1 KB = 1024 B • 1 MB = 1024 KB • 1 GB = 1024 MB • 1 TB = 1024 GB • 1 PB = 1024 TB
Bytes Converter — KB, MB, GB & TB Data Size Calculator
Type a data size in any unit and the page shows it in every other unit at once. The base toggle is the important detail: switch between IEC binary base (1024 — KiB, MiB, GiB, what RAM and OS file managers actually count) and SI decimal base (1000 — KB, MB, GB, what hard-drive manufacturers print on the box and what bandwidth is measured in). This is why a "2 TB" hard drive shows up as 1.82 TB in your operating system: the manufacturer used SI (1000⁴), the OS displays IEC (1024⁴), and 2 × 10¹² bytes / 1024⁴ ≈ 1.82. Useful when sizing storage, comparing cloud storage quotas, sanity-checking download progress, or reading file sizes in scripts that mix the two conventions.
About this tool
The two bases coexist for historical reasons. Computer engineers settled on powers of 1024 in the 1960s because that's what comes naturally from binary addressing (2^10 = 1024 ≈ 1000), and called them "kilobytes", "megabytes", etc. Hard-drive manufacturers in the 1990s started using strict SI powers of 1000 because the resulting numbers were larger (and looked better in marketing). The IEC fixed the ambiguity in IEC 60027-2 Amendment 2 (December 1998) by introducing distinct names: "kibibyte" (KiB) for 1024 bytes, "mebibyte" (MiB) for 1024², "gibibyte" (GiB), "tebibyte" (TiB), "pebibyte" (PiB). Reality on the ground in 2026: RAM is universally counted in IEC (your "16 GB" of RAM is actually 16 GiB = 17.18 GB SI), file sizes in macOS Finder since Mac OS X 10.6 Snow Leopard (28 August 2009) are SI (the "100 MB" file in Finder is 100,000,000 bytes), Windows uses SI-style labels (KB, MB) with IEC binary math (1024) — "100 MB" in Explorer is 104,857,600 bytes (which is technically 100 MiB) — and network bandwidth (Mbps, Gbps) is always SI bits per second (and yes, 8 bits per byte). Common reference points (binary): 1 KiB = 1,024 B, 1 MiB = 1,048,576 B, 1 GiB = 1,073,741,824 B, 1 TiB = 1,099,511,627,776 B. Decimal: 1 KB = 1,000 B, 1 MB = 1,000,000 B, 1 GB = 1,000,000,000 B, 1 TB = 1,000,000,000,000 B. The 2 TB → 1.82 TiB drift compounds: a "4 TB" drive is really 3.64 TiB.
- IEC binary base (1024) — KiB, MiB, GiB, TiB, PiB
- SI decimal base (1000) — KB, MB, GB, TB, PB
- Toggle between the two bases — explains hard-drive size discrepancy
- All units rendered simultaneously — see the same value in every column
- Quick presets for common sizes (RAM stick, SSD, HDD, cloud quota)
- Live conversion as you type — no Convert button
- Copy all results in either base with one click
- Useful for storage sizing, cloud quota comparison, script byte budgets
- Explains why your 2 TB drive shows 1.82 TB in your OS
- No upload — every conversion runs locally in your browser
Free. No signup. Your inputs stay in your browser. Ads via Google AdSense (consent required).
Frequently asked questions
Why does my "2 TB" hard drive show 1.82 TB in my OS?
The drive manufacturer used SI (decimal) prefixes — 1 TB = 1000⁴ = 10¹² bytes. Your operating system (Windows specifically, plus older Linux file managers and utilities such as `du` by default) reports binary (1024-based) prefixes — 1 TiB = 1024⁴ = 1,099,511,627,776 bytes — but commonly displays them as "TB" without distinguishing the base. Doing the math: 2 × 10¹² ÷ 1024⁴ = 1.82 TiB. The discrepancy compounds at larger scales: a "4 TB" drive displays as 3.64 TiB, an "8 TB" as 7.28 TiB, a "16 TB" as 14.55 TiB. Some of the apparent loss also includes filesystem overhead (NTFS / exFAT / ext4 metadata, typically 1-3%), but the dominant factor is the SI-vs-IEC base mismatch. macOS Finder switched to SI base in Mac OS X 10.6 Snow Leopard (28 August 2009), which is why your 2 TB drive shows as 2 TB on macOS but 1.82 TB on Windows.
When did the IEC formally distinguish KiB from KB?
The International Electrotechnical Commission published binary prefixes in IEC 60027-2 Amendment 2, approved December 1998 and published as a standard in 1999. The amendment introduced "kibi-", "mebi-", "gibi-", "tebi-", "pebi-", "exbi-", "zebi-", "yobi-" — formed from the SI prefix root plus "binary" — to denote powers of 1024 unambiguously. The international standard ISO/IEC 80000-13:2008 (Quantities and units, Part 13: Information science and technology) codified the binary prefix family alongside the SI decimal family. Adoption has been uneven: the standard is now widespread in physics, networking, file format specifications, and academic computer-science papers, but consumer-facing software still mixes both conventions. The original meaning of "kilobyte" as 1024 bytes remains common in operating systems and memory-related contexts (preserved by JEDEC Standard 100B.01 for memory), while hard-drive manufacturers, network bandwidth specifications, and post-2009 macOS use the strict SI meaning of 1000 bytes.
How does macOS report file sizes vs Windows in 2026?
Different default base. macOS Finder, since Mac OS X 10.6 Snow Leopard (28 August 2009), uses SI decimal — a "100 MB" file is exactly 100,000,000 bytes (100 × 10⁶). Windows Explorer uses binary math with SI-style labels — a "100 MB" file is 104,857,600 bytes (100 × 1024², which is technically 100 MiB). Linux file managers vary: GNOME Files, KDE Dolphin, and modern `ls` with `--si` follow SI; older `du` and `df` defaults are binary; many distributions ship `coreutils` with both `--si` (decimal) and `-h` (binary, default) flags. Network bandwidth and storage device capacity are always SI on every platform; RAM is universally counted in IEC binary on every platform. The practical upshot: when you see a discrepancy between a drive's box capacity and the OS display, the OS is almost always using a different base, not malfunctioning.
Why is "100 Mbps internet" not the same as "100 MB/s download"?
Two factors. First, network bandwidth is specified in bits per second (lowercase "b"), while file sizes are specified in bytes per second (uppercase "B"); 8 bits = 1 byte, so dividing the bandwidth by 8 gives the theoretical maximum byte-rate. Second, network bandwidth uses SI decimal — 100 Mbps = 100,000,000 bits/sec, no powers of 1024 anywhere (per IEEE Std 802.3). So 100 Mbps internet caps at 100 / 8 = 12.5 megabytes per second of theoretical raw download throughput. Real-world throughput is typically 80-95% of theoretical due to TCP overhead, packet headers, encryption, and contention — a "100 Mbps" connection commonly delivers 9-11 MB/s on well-tuned downloads (e.g., a 1 GB file in 90-110 seconds). The same logic applies to upload speeds, advertised Wi-Fi 6 peak rates (9.6 Gbps theoretical = 1.2 GB/s), and Ethernet (1000BASE-T = 1 Gbps = 125 MB/s peak).
How big is a typical 1080p video, MP3 audio, or PNG image?
Common reference points for sanity-checking storage and bandwidth budgets: a 1080p H.264 video at typical streaming bitrates ~5-10 Mbps runs ~2-4 GB per hour; 4K H.265 (HEVC) at ~25 Mbps streams is ~10-12 GB per hour. MP3 audio at 320 kbps (the highest common bitrate) is ~2.4 MB per minute; 128 kbps "good enough" audio is ~960 KB per minute. A typical photographic JPEG at quality 80-85 is 200 KB-2 MB depending on resolution; a UI screenshot PNG is 100 KB-1 MB; PDF documents range from 80 KB (text-only) to 30 MB+ (image-rich). RAM modules ship in 8/16/32 GiB binary capacities; modern desktops carry 32-64 GiB RAM; phones 6-16 GiB. SSDs are sold in SI (1000ⁿ) — a "500 GB" SSD has 500 × 10⁹ bytes = ~465 GiB before format overhead, dropping to ~455 GiB after typical filesystem metadata. microSD cards are sold by SI capacity but reformatting to FAT32 or exFAT loses ~2-3% to filesystem metadata.
Sources (7)
- International Electrotechnical Commission (IEC) (1998). IEC 60027-2 Amendment 2 — first formal definition of the binary prefixes kibi (Ki = 1024), mebi (Mi = 1024²), gibi (Gi = 1024³), tebi (Ti = 1024⁴), pebi (Pi = 1024⁵), exbi (Ei = 1024⁶), with names formed from the SI prefix root + 'binary'. IEC 60027-2:1972 / Amendment 2 approved December 1998, published 1999; superseded by ISO/IEC 80000-13:2008.
- International Organization for Standardization / IEC (2008). ISO/IEC 80000-13:2008 — Quantities and units, Part 13: Information science and technology (codifies the binary prefix family alongside the SI decimal family for byte-quantity expression). ISO/IEC Joint Technical Committee 1; supersedes the IEC 60027-2 binary prefix definitions.
- JEDEC Solid State Technology Association (2002). JEDEC Standard 100B.01 — Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits — retains the historical 'kilobyte = 1024 bytes' meaning specifically for memory contexts (RAM/ROM/cache), while acknowledging the IEC binary-prefix alternative. JEDEC Solid State Technology Association (Arlington VA); current revision continues memory-industry binary-meaning convention.
- Bureau International des Poids et Mesures (BIPM) (2019). The International System of Units (SI), 9th edition — defines SI decimal prefixes kilo (k = 10³), mega (M = 10⁶), giga (G = 10⁹), tera (T = 10¹²), peta (P = 10¹⁵) used by hard-drive manufacturers, network bandwidth, and post-2009 macOS file size reporting. 26th CGPM (November 2018), effective 20 May 2019; SI Brochure published by BIPM Sèvres.
- Apple Inc. (2009). Mac OS X v10.6 Snow Leopard — released 28 August 2009; introduced the file-size reporting shift from binary base (1024) to SI decimal base (1000) in Finder and the underlying Foundation framework, aligning with hard-drive manufacturer labels. Apple Worldwide Developers Conference unveil 8 June 2009; worldwide retail release 28 August 2009 (Mac OS X 10.6.0 build 10A432).
- Institute of Electrical and Electronics Engineers (IEEE) (2022). IEEE Std 802.3-2022 — Ethernet networking standard; bandwidth uniformly specified in bits per second using SI decimal prefixes (1 Mbps = 10⁶ bits/sec exactly, 1 Gbps = 10⁹ bits/sec exactly); 8 bits = 1 byte conversion required to translate to byte-rate. IEEE Standards Association (current revision IEEE 802.3-2022 supersedes earlier editions; the SI-bits-per-second convention has been continuous since IEEE 802.3-1985).
- World Wide Web Consortium (W3C) (2018). Web Content Accessibility Guidelines (WCAG) 2.1 — Success Criterion 4.1.3 Status Messages. W3C Recommendation 5 June 2018; carried unchanged into WCAG 2.2 (Recommendation 5 October 2023).
These are the original publications the formulas in this tool are based on. Locate them by journal name and year on Google Scholar or PubMed.
By Marco B. ·