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Data Size Converter

Convert between bytes, KB, MB, GB and TB in seconds.

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Frequently asked questions

Is a kilobyte 1,000 or 1,024 bytes?

Both, depending on who is counting. Storage manufacturers use 1,000 (the SI definition), while operating systems have traditionally used 1,024. That difference is why a '1 TB' drive shows as about 931 GB in Windows.

What are KiB, MiB and GiB?

The unambiguous binary units: a KiB is exactly 1,024 bytes, a MiB 1,024 KiB. They exist precisely to remove the confusion above, and are worth using in technical documentation.

What is the difference between a megabit and a megabyte?

Eight to one. Internet speeds are quoted in megabits per second while file sizes are in megabytes, so a 100 Mbps connection downloads at about 12.5 MB/s at best — the single most common source of 'my internet is slower than advertised'.

Pro tips

  • Read a Roman numeral left to right and subtract only where a smaller symbol precedes a larger one; everything else adds.
  • Check whether a stated file size is decimal or binary before concluding storage is missing — the difference is about 7% at terabyte scale.
  • Remember that MPG and L/100km invert. Comparing two cars across the two systems without converting will reliably pick the wrong one.
  • Use the binary units (KiB, MiB, GiB) explicitly when precision matters; they exist specifically to remove this ambiguity.
  • Watch for US and imperial gallons in fuel figures — they differ by about 20%, which is more than the difference between most cars.

About Everyday Converters

Each of the three has a trap. Roman numerals carry no zero and no place value, a kilobyte means 1,000 or 1,024 bytes depending on who is counting, and fuel economy inverts between the two systems — a higher MPG is better while a higher L/100km is worse.

Convert data sizes between bytes, KB, MB, GB and TB using 1024-based steps — useful for sizing files, downloads and storage quotas. The conversion runs locally in your browser.

Convert numbers to and from Roman numerals, change data sizes between bytes, kilobytes, megabytes, gigabytes and beyond, and translate fuel economy across MPG, L/100km and km/L. It bundles three common conversions you reach for surprisingly often.

Everything works offline in your browser. Decode a Roman numeral on a monument, size a file or download, or compare a car's fuel efficiency between regional standards in seconds.

Roman numerals have no zero and no place value, which is why they are read by addition and subtraction rather than by position. A smaller numeral before a larger one is subtracted — IV is four, IX is nine — and only certain pairs are permitted in the standard form, which is why 1999 is MCMXCIX rather than the tidier-looking MIM. That constraint is the usual reason a hand-written conversion disagrees with a correct one.

Data sizes are ambiguous by convention rather than by error. Drive manufacturers count a gigabyte as 1,000,000,000 bytes while many operating systems report binary gibibytes of 1,073,741,824, and the gap widens as the units grow — which is the entire explanation for a 1 TB drive showing up as roughly 931 GB with nothing missing and nobody at fault. Fuel economy carries a different trap: MPG and L/100km run in opposite directions, so a higher number is better in one and worse in the other.

Common use cases

  • Working out why a drive shows less capacity than advertised
  • Converting a download speed into a realistic transfer time
  • Checking whether a file fits a storage or upload quota
How it comparesEach of these three has dedicated single-purpose sites, and needing two of them means opening two tabs. Bundling the conversions people actually reach for occasionally is the point; a specialist tool is better if you do one of them constantly.