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Each step = ×1,024 (binary) or ×1,000 (decimal/SI)Byte= 8 bits (B)KB= 1,024 bytes (Kilobyte)MB= 1,024 KB (Megabyte)GB= 1,024 MB (Gigabyte)TB= 1,024 GB (Terabyte)5 × 1,024 = 5,120 MB. 5,120 × 1,024 = 5,242,880 KB.
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Convert between data size units (KB, MB, GB, TB, KiB, MiB, GiB). Calculate transfer times and compare storage capacity for different media.
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Convert between bytes, kilobytes, megabytes, gigabytes, terabytes and binary units
Data size measures the amount of digital information stored or transmitted. The most fundamental unit is the bit (binary digit: 0 or 1). Eight bits form one byte, the basic addressable unit of computer memory.
There are two competing systems for expressing data sizes — and confusion between them causes one of the most common tech frustrations: why a hard drive appears smaller in Windows than on the box.
Decimal (SI) system: Used by storage manufacturers. Prefixes follow the International System of Units — kilo = 1,000, mega = 1,000,000. A manufacturer's "1 TB" hard drive contains exactly 1,000,000,000,000 bytes.
Binary (IEC) system: Used by operating systems. Prefixes are powers of 2 — kibi = 1,024, mebi = 1,048,576. Windows reports storage in GiB but labels them "GB", causing the apparent size discrepancy.
Everyday examples: a 4K video is ~50 GB/hour; an MP3 song is ~3–5 MB; a high-resolution photo is ~3–8 MB; a Blu-ray disc holds 50 GB; a modern smartphone ships with 128–512 GB of storage.
| Unit | Decimal (SI) | Binary (IEC) | Difference (%) |
|---|---|---|---|
| Kilo | 1 KB = 1,000 bytes | 1 KiB = 1,024 bytes | 2.4% |
| Mega | 1 MB = 1,000,000 bytes | 1 MiB = 1,048,576 bytes | 4.86% |
| Giga | 1 GB = 10⁹ bytes | 1 GiB = 2³⁰ bytes | 7.37% |
| Tera | 1 TB = 10¹² bytes | 1 TiB = 2⁴⁰ bytes | 9.95% |
| Peta | 1 PB = 10¹⁵ bytes | 1 PiB = 2⁵⁰ bytes | 12.59% |
IBM 305 RAMAC — first commercial hard disk (5 MB, the size of two refrigerators; leased for $3,200/month)
IBM PC launches with 320 KB floppy disk drive; popularizes KB/MB units in consumer computing
IEC introduces KiB/MiB/GiB notation (IEC 80000-13) to formally distinguish binary from decimal prefixes
First 1 GB USB flash drive released by Trek Technology at a retail price of ~$350
US NIST officially adopts IEC binary prefixes in formal scientific publications (SP 330)
World creates 120 zettabytes of data; 100 GB storage costs under $3 (50 million× cheaper than 1956)
120 zettabytes of data created in 2023; 5x growth projected by 2025
Visit IDC Data Age 2025 Report →Official international definition of KiB, MiB, GiB binary notation to prevent ambiguity
Visit IEC 80000-13:2021 Standard →US National Institute of Standards adoption of binary prefixes for data measurement
Visit NIST SI Guide (SP 330) →My 1TB hard drive is broken — Windows shows only 931 GB
Drive manufacturers use decimal TB (10¹² bytes), but Windows shows binary GiB. 1 TB = 931.3 GiB — your drive is perfectly fine
1 kilobyte is always 1,024 bytes
Since the 1998 IEC standard: 1 KB = 1,000 bytes (decimal). The old 1,024-byte unit is now correctly called 1 KiB (kibibyte)
Internet speed in Mbps and file size in MB are the same thing
Internet speeds are in MEGABITS per second. A 100 Mbps connection downloads only 12.5 MB/sec — divide by 8, since 1 byte = 8 bits
Storage is storage — all gigabytes are equal
Hard drives (decimal), RAM (binary), and SSDs may use different sizing conventions. Always check whether specs use GB (decimal) or GiB (binary)
KB (kilobyte) = 1,000 bytes in the decimal SI system. KiB (kibibyte) = 1,024 bytes in the binary IEC system. The IEC introduced the KiB notation in 1998 to eliminate the century-old ambiguity.
In decimal (SI): 1 GB = 1,000,000,000 bytes (10⁹). In binary (IEC): 1 GiB = 1,073,741,824 bytes (2³⁰). The difference is about 7.4%.
Drive manufacturers measure in decimal GB (10⁹ bytes), while Windows reports in binary GiB (2³⁰ bytes) but calls them GB. A 1 TB drive = 931.3 GiB — nothing is missing.
Transfer time (seconds) = File size in bits ÷ Connection speed in bps. Remember: 1 byte = 8 bits. For a 100 MB file over 100 Mbps: (100 × 8) ÷ 100 = 8 seconds.
1 zettabyte = 10²¹ bytes = 1,000 exabytes = 1,000,000 petabytes. The entire internet traffic per year is measured in zettabytes. IDC estimated 120 ZB of data was created in 2023.
1 GB = 1,000 MB (decimal/SI). 1 GiB = 1,024 MiB (binary/IEC). The decimal definition is used by storage manufacturers; the binary by most operating systems.
Mbps = Megabits per second (lowercase b). MBps = Megabytes per second (uppercase B). Since 1 byte = 8 bits, 100 Mbps = 12.5 MBps. Always check the notation in network specs.
At typical 128 kbps MP3 quality (~1 MB/min), a 4-minute song ≈ 4 MB. So 1 GB ≈ 250 songs. At 320 kbps (high quality), 1 GB ≈ 100 songs.
Commonly used: yottabyte (YB, 10²⁴). Beyond that: ronnabyte (10²⁷) and quettabyte (10³⁰) were officially added by BIPM in 2022. The yobibyte (YiB, 2⁸⁰) is the binary equivalent.
Older versions of Windows showed storage in GiB but labeled it GB. macOS switched in 2009 to use decimal GB matching drive specs. A file both systems show is the same size — only the label convention differs.
IEC 80000-13:2021 defines binary prefixes: kibi (Ki, 2¹⁰), mebi (Mi, 2²⁰), gibi (Gi, 2³⁰), tebi (Ti, 2⁴⁰), pebi (Pi, 2⁵⁰), exbi (Ei, 2⁶⁰), zebi (Zi, 2⁷⁰), and yobi (Yi, 2⁸⁰).
Divide bits by 8 to get bytes. Multiply bytes by 8 to get bits. Example: 1,000 bits = 125 bytes. A 1 Mbps network speed = 0.125 MB/s download speed.
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