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Roman Numeral Converter

Convert numbers to and from Roman numerals instantly.

Processed locally — nothing is uploaded

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 Roman numerals and Roman numerals back to numbers, from 1 to 3999, with validation of canonical forms like MMXXIV. It works offline 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.

Learn how this works

Everyday Calculations & Conversions Made SimpleConvert units and time zones, and calculate age, BMI, discounts and loan EMIs — a plain-English guide with free in-browser tools.7 min read

Frequently asked questions

How does subtractive notation work?

A smaller numeral before a larger one is subtracted: IV is 4 and IX is 9, rather than IIII and VIIII. Only I, X and C are used this way, and only before the next two higher symbols.

What is the largest number that can be written?

3,999 (MMMCMXCIX) using standard numerals, because there is no symbol above M and no more than three may repeat. Larger values historically used a bar above a numeral to mean multiply by a thousand.

Why is there no zero?

The system was built for counting and commerce, where nothing simply was not written down. Zero as a number arrived in Europe much later via Arabic numerals, which is a large part of why they displaced Roman ones.

Common Use Cases

  • •Reading a date on a building, monument or film credit
  • •Working out a Super Bowl or monarch's number
  • •Checking a numeral for a tattoo or engraving before committing

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