Roman Numeral Converter
Convert an Arabic number to Roman numerals or a Roman numeral back to a number.
Supports integers from 1 to 3,999,999, including overline notation for large values.
Updated August 13, 2026
Introduction / overview
The Roman Numeral Converter switches between ordinary Arabic (decimal) numbers and Roman numerals in either direction. Type 2026 and it writes MMXXVI; flip the direction, type MMXXVI, and it reads the value back as 2026 — with support all the way up to 3,999,999.
The classic question this solves: “What year does MMXXVI on this building mean?” — or its reverse, “How do I write 2026 in Roman numerals for an invitation or engraving?”
Who is this for?
- Anyone decoding dates on buildings, monuments, clocks, film credits, or book prefaces.
- Students and hobbyists checking their own conversions or learning the notation.
- Engravers, designers, and writers formatting titles, chapters, and year numbers.
Because the conversion runs both ways and rejects anything that isn't a valid Roman numeral, you can use it to check what you've just read just as easily as you use it to write. In the Arabic → Roman direction the calculator even shows its working, breaking the number into place values so you can see exactly how the symbols are assembled.
How to use / quick start
- 1Pick the direction. The default is Arabic number to Roman numerals; choose Roman numerals to Arabic number to go the other way.
- 2Enter a whole number from 1 to 3,999,999, or a Roman numeral using the letters I, V, X, L, C, D, M. Lowercase works too — reads the same as .
- 3Read the converted value in the Result box. It updates as you type, so you can experiment freely.
Example 1 — write 2026 as Roman numerals
Enter . The calculator splits it into place values and converts each one:
In the Arabic → Roman direction you'll also see this breakdown spelled out in the Explanation panel.
Example 2 — read MMXXVI back as a number
Switch to Roman numerals to Arabic number and type . Read left to right, each symbol adds its value:
Because the letters are in descending order here, it's a straight addition — the subtraction rule in the next section covers the cases where a smaller symbol comes first.
How to interpret the results
- The derived value appears in the Result box. In the Arabic → Roman direction, the Explanation panel shows the place-by-place breakdown so you can follow the logic.
- Values of 4,000 and above use the overline notation — a bar over a symbol — so don't mistake a bar for an accent mark.
- A quick sanity check: type a year you already know, such as , and confirm it reads .
Calculation method / formula
The symbols
Modern Roman numerals use seven letters, each with a fixed value. The numeral's value is the sum of the symbols, with one exception described below.
Additive and subtractive rules
When symbols run from largest to smallest, they simply add up:
But when a smaller symbol sits before a larger one, it is subtracted. The only subtractive pairs in standard form are :
In general, each symbol contributes its value as unless a larger symbol follows it, in which case it contributes .
Writing a number as Roman numerals
The writing direction splits the number into its place values, converts each place, then joins the symbols from largest to smallest. For example:
Reading works in reverse: parse each symbol (or subtractive pair) and add the results. Both directions are handled automatically by the calculator, so you never have to rebuild the string by hand.
Large numbers — the overline (vinculum)
Standard Roman numerals run out at (). To go further, the calculator uses the overline (also called the vinculum): a bar over a symbol multiplies its value by 1,000.
With this notation the calculator reaches , using the same addition and subtraction rules on top of the overline. The bar-over-symbol convention is a long standing one — see the Roman numerals overview on Wikipedia for the standard symbol values and the vinculum notation.
Roman numerals are just one way to represent a number. If you're comparing how other numeral systems are written — binary, octal, or hexadecimal — our Binary Converter and Decimal to Hexadecimal Converter use the same convert-and-read-back approach in their own bases.
Limitations / disclaimers
What the converter covers
- Whole positive integers only. The Roman system has no symbol for zero and no standard way to write arbitrary fractions, so 0, negatives, and decimals are rejected.
- Writing range is 1 to 3,999,999 (values above 3,999 use the overline). Reading accepts standard numerals up to 3,999 — nearly everything you'll meet on a clock face or building.
- Standard form is expected. The calculator writes the modern subtractive form (, not ). Decorative or historical variants you may see in the wild — like the on many clock faces — aren't recognized.
- Exact, no rounding. A valid conversion is always exact — there's no approximation involved.
Frequently asked questions
Why is there no Roman numeral for zero?
Roman numerals are an additive counting system built around fixed symbols, so there is no symbol for “nothing” and no place-keeping zero the way Arabic numerals have. That's exactly why the converter rejects .
Why is 4 written “IV” and not “IIII”?
Modern standard form uses subtractive notation: placing before means . It's shorter and less easy to misread. That said, the additive form has a long tradition on clock faces, so don't be surprised to see it there.
How are numbers above 3,999 written?
With an overline: a bar over a symbol multiplies it by 1,000, so . The calculator uses this to reach — for example, is written .
Related Calculators
Scale Calculator
Calculate scale factors and convert scaled or real dimensions for length, area, and volume.
Text to NATO alphabet
Transform text into the NATO phonetic alphabet for oral transmission. Convert letters A–Z into Alpha/Bravo/Charlie… and copy instantly.
Text to ASCII binary
Convert text to ASCII (8-bit) binary and convert ASCII binary back to text. Clean input automatically and copy results instantly.
Text to Unicode
Convert text to Unicode decimal HTML entities (e.g., A) and convert them back to text. Runs locally in your browser with one-click copy.
Escape/unescape HTML entities
Escape and unescape HTML entities for <, >, &, ", and ’. Runs locally in your browser with instant copy.
Integer Base Converter
Convert an integer between bases 2–64 (binary, octal, decimal, hexadecimal, base64, and custom). Runs locally in your browser.