File Size Converter

Why a "megabyte" can mean two different things

The biggest source of confusion in file sizes is that the prefix "mega" has two competing definitions. In the decimal (SI) system, each step up multiplies by 1,000: a kilobyte is 1,000 bytes, a megabyte is 1,000,000 bytes. In the binary (IEC) system, each step multiplies by 1,024 — because computer memory is addressed in powers of two — and the units get distinct names: kibibyte (KiB), mebibyte (MiB), gibibyte (GiB). This tool lets you convert in either system and switch between them with a single toggle, so you always know which definition you are using.

The unit ladders, side by side

Both ladders also start from the bit (one binary digit) and the byte (8 bits), which is why the tool can convert between bits and bytes too — useful when a network speed is quoted in megabits but a download size is in megabytes. The gap between the two systems widens at every level: at the gigabyte scale a "GB" and a "GiB" already differ by about 7%, which is exactly why a "1 TB" drive shows as roughly 931 GiB in your operating system.

A worked example

Type 1 into the Gigabytes field in decimal mode. The tool instantly fills every other field from the same underlying value: 1 GB equals 1,000 MB, 1,000,000 KB, 1,000,000,000 bytes, and 8,000,000,000 bits. Now switch the toggle to binary and enter 1 in Gibibytes: you get 1,024 MiB, 1,048,576 KiB, and 1,073,741,824 bytes. The "all conversions at a glance" table below the inputs lists every unit at once, so a single number you enter is shown across the whole ladder without any extra clicks.

How the precision is kept honest

File sizes can be enormous, and ordinary floating-point math drifts on big numbers. This converter holds the value internally as a high-precision integer of bits (scaled up by a large factor) using arbitrary-precision arithmetic, then formats each field for display. That means converting 5 PB down to bits and back does not accumulate rounding error. Very large or very small results are shown in a readable form — grouped with thousands separators in the normal range, and switched to scientific notation only at extreme magnitudes.

A built-in sense of scale

Numbers like "37,600,000,000 bits" are hard to picture, so the tool shows a plain-language reference for whatever you enter — for example it will note that around 4.7 GB is "a single-layer DVD," 25 GB is "a Blu-ray disc," and 1 TB is "a typical laptop hard drive." It picks the closest landmark to your value, giving you an intuitive anchor instead of just a wall of digits.

Common mistakes

• Mixing bits and bytes. A "100 Mbps" connection is 100 megabits per second, which is only 12.5 megabytes per second. Confusing the two makes downloads seem eight times slower than expected. Convert through the bits field to keep them straight.
• Assuming your OS uses decimal. Storage marketers use decimal (so a drive is "1 TB"), but Windows reports binary (so it shows ~931 GB). Nothing is missing — the units differ. Use binary mode to reproduce what your OS displays.
• Trusting "MB" without context. If a spec sheet says MB but means MiB, your numbers will be off by a few percent. When precision matters, ask which system is meant.

Practical uses and privacy

Estimate how many photos fit on a memory card, check whether a video will fit an email attachment limit, convert a bandwidth quote into a download time, or reconcile a vendor's "GB" with your computer's "GiB." All math happens in your browser — no value you type is sent anywhere — so it works instantly and offline.