File Size Calculator

File Size Calculator: convert file size instantly. Full formula, unit table, and worked example.

A data storage converter switches between bits, bytes, kilobytes (KB), megabytes (MB), gigabytes (GB), terabytes (TB), petabytes (PB), and their binary equivalents (kibibytes, mebibytes, gibibytes). Digital storage is fundamental to computing, networking, cloud storage pricing, and data transfer planning. The distinction between binary prefixes (1 KB = 1,024 bytes in computing) and decimal prefixes (1 KB = 1,000 bytes in storage marketing) causes persistent confusion when comparing advertised and actual storage capacities.

Use related pages when the same quantity appears in another convention: compare Data Conversion Calculator,Bytes to MB Calculator, and Storage Calculator while keeping the unit definition, reference conditions, and rounding rule visible. Conversion is a transparent change of representation, not evidence that the underlying measurement or model is accurate.

For energy, temperature, pressure, and digital data, a familiar label can hide different boundaries. Check whether the value describes a physical quantity, a rate, a storage capacity, a transfer speed, or a derived result. Preserve the original input and the unrounded intermediate value, especially when the converted number will feed another formula, a purchase, a technical specification, or a safety or regulatory decision.

Check the direction as well as the magnitude: converting from a larger unit to a smaller unit usually increases the numerical value, while the reverse usually decreases it. That simple sense check catches many inverted factors. Then compare the result with a familiar reference, such as a litre, kilogram, kilometre, degree, pound, megabyte, or standard atmospheric pressure. If the comparison is surprising, inspect the source unit, prefix, regional convention, and whether the calculator expects a rate or a total before accepting the displayed number.

Some relationships are exact by definition, while others are rounded references or depend on conditions. A temperature interval is not interpreted exactly like an absolute temperature, a decimal data prefix may be decimal or binary, and energy or pressure values can be tied to a stated standard. Derived quantities need the same care: square units require the conversion factor to be squared, and rates require both the numerator and denominator to be identified. Keep those definitions with the result so another reader can reproduce the conversion without guessing what the label meant.

Enter the data size and select the source unit.
Specify whether you want binary (1 KB = 1,024 bytes, used by operating systems) or decimal (1 KB = 1,000 bytes, used by storage manufacturers).
The converter shows equivalents in all common units.
For data transfer: divide file size by transfer speed to estimate time — e.g. 1 GB file at 10 MB/s = 100 seconds.

Data conversion factors

Decimal (SI, storage marketing): 1 KB = 1,000 B; 1 MB = 1,000 KB; 1 GB = 1,000 MB; 1 TB = 1,000 GB

Binary (IEC, OS reporting): 1 KiB = 1,024 B; 1 MiB = 1,024 KiB; 1 GiB = 1,024 MiB; 1 TiB = 1,024 GiB

Transfer time = File size / Transfer rate (match units — bits vs bytes: 1 byte = 8 bits)

Network speed is quoted in Mbps (megabits per second). Download time = file size (MB) / (speed Mbps / 8)

Data size reference

Common file and storage sizes

Text email: ~5 KB. MP3 song (4 min, 128 kbps): ~4 MB. HD photo (JPEG): ~3–5 MB. 4K video (1 hour): ~50–100 GB. Blu-ray movie: ~25–50 GB. Full installation of Windows 11: ~20 GB. iPhone 15 base storage: 128 GB. High-end gaming PC SSD: 1–4 TB. Enterprise data centres: petabytes to exabytes (1 EB = 1,000 PB = 1,000,000 TB).

Conversion tips and best practices

A "1 TB" hard drive sold in a store contains 1,000,000,000,000 bytes — but your OS (using binary) shows it as approximately 931 GiB.
Internet speeds in "100 Mbps" are in megabits per second — divide by 8 to get MB/s. A 100 Mbps connection downloads approximately 12.5 MB per second.
Streaming: Netflix 4K requires ~15–25 Mbps; HD requires ~5 Mbps; SD requires ~3 Mbps.
Cloud storage pricing is always in decimal gigabytes (1 GB = 10⁹ bytes) — the same convention used by manufacturers.

The total amount of data stored globally reached approximately 120 zettabytes (ZB) in 2023 — a zettabyte = 10²¹ bytes = 1 billion terabytes.
Google processes approximately 20 petabytes of data per day. The Human Genome Project data is approximately 200 GB per sequenced genome.
The first commercial hard drive (IBM 350, 1956) stored 3.75 MB and was the size of a refrigerator; a modern USB flash drive stores 1 TB — a 266 million times improvement in density.

Common mistakes to avoid

Confusing bits and bytes — internet speeds in "100 Mbps" are megabits (100 Mb/s), not megabytes (12.5 MB/s). Many people overestimate download speed by a factor of 8.
Expecting a "1 TB" drive to show 1 TB in your operating system — binary-counting OSes will show approximately 931 GB due to the binary/decimal prefix difference.
Mixing MB/s (megabytes per second) and Mbps (megabits per second) in transfer calculations — always confirm which unit is used before computing download time.

Storage capacity advertising standards vary by jurisdiction. In the US, the FTC has allowed decimal (10⁹ bytes = 1 GB) definitions for hard drive advertising. Operating system reporting uses binary (2³⁰ bytes = 1 GiB). For regulated data capacity requirements (cloud SLAs, data retention compliance), confirm which definition applies.