How do I convert a number to a Roman numeral?

Open the 123 to Roman tab, type a whole number from 1 to 3,999,999, and the numeral appears at once. Click Copy to use it, or open Breakdown to see its parts.

Why does the converter say Invalid Roman numeral?

Reverse conversion only accepts standard form. Non-standard strings such as IIII instead of IV are rejected, as are letters outside I, V, X, L, C, D and M.

What is the largest number it can convert, and how are numbers above 3999 written?

The maximum is 3,999,999. Above 3999 it uses vinculum notation, where a bar over a letter multiplies it by 1000, so 5000 is V with an overline.

How do I write a date like a wedding date in Roman numerals?

Use the Date to Roman tab, pick the date, then choose the Order (day, month, year in any of three orders) and a Separator. Day, month and year are each converted separately.

How do I convert a Roman numeral from a movie credit back to a year?

Open the Roman to 123 tab and type the numeral, for example MMXXIV. The Decimal value appears immediately. It must be a valid standard numeral.

Yes. Every tool is free to use, with no account and no credit card. The work runs on your device rather than on our servers, which is what keeps it free to run.

Does it work on mobile?

Yes. It runs in current mobile browsers on iOS and Android, with nothing to install.

🏛️

Free Roman Numeral Converter

Convert numbers to Roman numerals and back. Standard numerals cover 1–3999, with vinculum notation extending the range to 3,999,999.

Runs in your browserNo sign-up, no pop-upsNo login requiredFree forever

Works offline once loaded

Decimal number (1–3,999,999)

Roman numeral

MMXXVI

Breakdown

MM2000+XX20+V5+I1

Common values

Reference table (click to copy)

Roman numeral rules: I=1, V=5, X=10, L=50, C=100, D=500, M=1000.

Subtractive notation: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Standard numerals max out at MMMCMXCIX (3999).

Vinculum: a bar over a numeral multiplies it by 1000 (V̅ = 5000, X̅ = 10000, M̅ = 1,000,000), extending the range to 3,999,999.

Common uses

Convert Dates to Roman NumeralsWrite years, wedding dates, and anniversaries in Roman numerals for invitations and commemorative designs.
Roman Numerals for Outlines and DocumentsGenerate the correct Roman numerals for document outlines, chapters, and formal section numbering.
Decode Roman Numerals in Movies and TVDecode Roman numeral sequel numbers, Super Bowl editions, and film copyright years.
Learn Roman Numerals for SchoolPractice converting between Roman numerals and decimal numbers for history, math, and classical studies.
Roman Numerals for Design and TattoosGet accurately formatted Roman numerals for graphic design, clock faces, tattoos, and monograms.

How It Works

All conversion runs in your browser via a hand-written, zero-dependency algorithm — no server request is made. A fixed lookup table of 13 symbol-value pairs (M=1000 down to I=1) drives both directions of conversion, and canonical validation round-trips the result to reject non-standard input.

1
Lookup table drives conversion
The tool defines 13 symbol-value pairs — M, CM, D, CD, C, XC, L, XL, X, IX, V, IV, I — in descending order. To convert a decimal number, it walks this list and repeatedly subtracts each value while appending the matching symbol, the standard greedy Roman numeral algorithm.
2
Canonical validation on reverse conversion
When converting a Roman numeral back to a number, the parser uses the subtractive rule (a smaller value before a larger one is subtracted, not added), then immediately re-encodes the result and compares it to the original input. Any non-canonical string — for example IIII instead of IV — is rejected.
3
Vinculum notation extends the range to 3,999,999
Numbers above 3,999 use vinculum notation: the thousands portion is converted to basic Roman, then a Unicode combining overline character (U+0305) is appended to each letter to render the traditional overbar that signifies multiplication by 1,000. For example, 5,000 is rendered as V with an overline.
4
Date mode converts each component independently
In date mode, the tool parses the selected date into day, month, and year integers, converts each one through the same toRoman function, then joins them with the chosen separator (middle dot, hyphen, slash, or space) in the chosen order (DMY, MDY, or YMD).

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Free Roman Numeral Converter

Common uses

How It Works

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Frequently Asked Questions