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Everyday Converters

Roman numerals, data sizes (KB/MB/GB) and fuel economy conversions.

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Frequently asked questions

What range of Roman numerals is supported?

Standard Roman numerals from 1 to 3999, converted both ways, with validation of canonical forms like MMXXIV. Roman numerals in this range cover most historical dates, ancient texts, and modern use cases (like book chapters or movie sequels). The converter validates that Roman numerals follow canonical form rules — for example, always subtracting (IV for 4, not IIII) — ensuring the converted output is correctly formatted. You can convert decimal to Roman (2024 becomes MMXXIV) or Roman to decimal (MCMXC becomes 1990) instantly.

Are data sizes based on 1000 or 1024?

The data-size converter uses 1024-based steps between units, the convention common in computing for KB, MB, GB and TB. The computing convention (1 KB = 1024 bytes) differs from the decimal convention used in storage marketing (1 GB = 1000 MB), which is why your 1 TB drive shows as only ~931 GB in operating systems. This tool uses the technical computing standard, so 1 MB = 1024 KB = 1048576 bytes, matching what developers and system administrators expect. This convention also aligns with binary-based calculations like data transfer rates and memory allocation.

Can it convert fuel economy?

Yes — translate between MPG, litres per 100 km and km per litre to compare efficiency across regions. Different countries use different fuel efficiency metrics — the US uses MPG (miles per gallon), Europe uses L/100km (liters per 100 kilometers), and some regions use km/L (kilometers per liter). These metrics are not linear conversions, so direct comparison is impossible without calculation. The tool converts between all three formats instantly, allowing you to compare a US car's 30 MPG rating against a European car rated at 7.8 L/100km to determine which is more efficient.

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 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

  • Decoding a Roman numeral date on a building, monument, film credit or clock face.
  • Working out whether a download will fit the space a device reports as free.
  • Comparing the fuel economy of two cars advertised under different regional standards.
  • Converting a copyright or edition year written in numerals for a citation.
  • Estimating transfer times or storage costs where the unit convention affects the answer.
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.