Every time you check your phone's storage, download a file, or buy an external hard drive, you're dealing with data size units. But what exactly is the difference between a megabyte and a mebibyte? Why does your 256 GB phone only show 238 GB of usable space? This guide answers all these questions and teaches you to convert between any digital storage unit.
Digital data is measured in bytes. A byte consists of 8 bits, and it's the basic addressable unit of memory in most computer systems. From there, units scale up using prefixes — but there are two competing systems, which is the source of widespread confusion.
This is the single most important concept in data size conversion. There are two ways to scale up from bytes, and they produce different results:
Used by storage manufacturers (hard drives, SSDs, USB drives) and networking standards. Each step multiplies by 1,000.
1 KB = 1,000 bytes → 1 MB = 1,000,000 bytes → 1 GB = 1,000,000,000 bytes
Used by operating systems (Windows, macOS, Linux) and RAM specifications. Each step multiplies by 1,024 (2¹⁰).
1 KiB = 1,024 bytes → 1 MiB = 1,048,576 bytes → 1 GiB = 1,073,741,824 bytes
The International Electrotechnical Commission (IEC) introduced the binary prefixes (kibi-, mebi-, gibi-) in 1998 to distinguish them from the decimal prefixes (kilo-, mega-, giga-). However, most operating systems still display "KB" when they actually mean "KiB," which is why people see confusing discrepancies.
Divide by 1,000 when dealing with storage device capacities. A 16,000 MB flash drive equals 16 GB in manufacturer terms.
Divide by 1,024 when your operating system reports the values. A file that Windows shows as 5,000 MB is actually about 4.88 GiB.
Internet speeds are measured in bits per second (Mbps), while file sizes are in bytes. An 100 Mbps connection downloads at most 12.5 MB/s (100 ÷ 8), not 100 MB/s. This is a common source of confusion.
This is the question that brings most people to a data size converter. Here's exactly what happens:
Nobody is deceiving you — both numbers are mathematically correct, just using different unit systems.
When comparing a 256 GB SSD with a 512 GB option, understanding that the usable space will be about 238 GB and 476 GB respectively helps you make informed decisions. For smartphones, factor in the operating system's overhead — a 128 GB iPhone typically offers about 117 GB of user-accessible storage.
Your ISP advertises speeds in Mbps (megabits per second), but files download in MB/s (megabytes per second). A 500 Mbps plan delivers a theoretical maximum of 62.5 MB/s. To download a 50 GB game, you'd need 50,000 MB ÷ 62.5 = 800 seconds, or about 13.3 minutes under ideal conditions.
Google Drive offers 15 GB free. How much can you store? Roughly 3,000 photos, 1,875 songs, or 3 HD movies. Planning cloud backup for your photo library of 50,000 images at 4 MB each means you need about 200 GB of cloud storage — a paid plan on any major provider.
Web hosts charge for both storage and bandwidth. A website with 100 pages averaging 2 MB each uses 200 MB of storage. If the site gets 10,000 visitors per month who view 5 pages each, that's 50,000 pageviews × 2 MB = 100 GB of monthly bandwidth transfer.
RAM is always measured in binary units. 16 GB of RAM is actually 16 GiB (17,179,869,184 bytes). This is why RAM capacities are always powers of 2 (4, 8, 16, 32, 64 GB) — they naturally align with the binary system.
It depends on the system. In the decimal (SI) system used by hardware manufacturers and networking standards, 1 GB = 1,000 MB. In the binary system used by operating systems, 1 GiB = 1,024 MiB. Most people (and most software) say "GB" when they mean "GiB," which creates confusion. Our converter lets you choose which system to use.
KB (kilobyte) is a decimal unit equal to 1,000 bytes. KiB (kibibyte) is a binary unit equal to 1,024 bytes (2¹⁰). The IEC introduced the binary prefixes in 1998 to eliminate this confusion. In practice, Windows shows "KB" but calculates in KiB, macOS now uses decimal KB since version 10.6 (Snow Leopard), and Linux varies by tool.
A 4K movie ranges from 20 GB to 100+ GB depending on length, bitrate, and compression. Streaming services like Netflix use heavily compressed 4K at about 7-15 GB per 2-hour movie. A 4K Blu-ray rip can be 50-80 GB. Uncompressed 4K video runs about 400 GB per hour, which is why compression is always used for consumer content.
Storage manufacturers use decimal gigabytes (1 GB = 1,000,000,000 bytes) while operating systems display binary gigibytes (1 GiB = 1,073,741,824 bytes) but label them as "GB." A 1 TB drive (1 trillion bytes) shows as ~931 GB in Windows. Additional space is also reserved for the file system format (NTFS, APFS, ext4) and recovery partitions.
The largest officially adopted units are ronnabyte (RB, 10²⁷ bytes) and quettabyte (QB, 10³⁰ bytes), approved by the General Conference on Weights and Measures in 2022. In practice, yottabytes (YB, 10²⁴ bytes) and zettabytes (ZB, 10²¹ bytes) are the largest commonly referenced units. For context, all data created globally in 2024 is estimated at about 120 zettabytes.