Convert between Arabic numbers and Roman numerals. Free, private, runs in your browser.
100% private — your files never leave your browser. All processing happens locally on your device.
Quick reference
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000
Values above 3,999 are rendered using vinculum notation (combining overline, which multiplies by 1,000).
Modern life still uses Roman numerals constantly — movie copyright years (MMXXIV = 2024), Super Bowl numbers, book chapter headings, clock faces, royal succession (Henry VIII), and pharmaceutical drug-dosage levels. The system is inconvenient for arithmetic — that's why we moved on — but it's more visually distinctive than Arabic digits, which is why it survives where tradition or visual hierarchy matter more than convenience.
Roman numerals use seven letters: I (1), V (5), X (10), L (50), C (100), D (500), M (1000). Values are usually additive — III is 3, VII is 7 — except where a smaller value precedes a larger one, in which case it's subtracted. IV (4), IX (9), XL (40), XC (90), CD (400), CM (900). The subtractive rules keep the written form compact: 1999 is MCMXCIX (seven characters), not 1000 nines.
Letters I, X, C, M can repeat up to three times (III, XXX, CCC, MMM). V, L, D never repeat — V+V would just be X. Only I can subtract from V and X; only X can subtract from L and C; only C can subtract from D and M. So IL (49) is wrong — the right form is XLIX. VX (5 subtracted from 10) isn't a valid form; use V directly or X − V. The tool validates all these rules and returns a clear error pointing at the broken one.
Classical Roman numerals max out at MMMCMXCIX = 3999. For larger numbers, Romans used a vinculum — a horizontal bar over a letter that multiplied its value by 1000. This calculator supports numbers up to 3,999,999 by rendering the thousands part with Unicode combining overline characters. So 5000 becomes V̄ (V with overline), 10000 becomes X̄, and so on. The rendered output copies into plain text correctly in modern font stacks.
All parsing and conversion happens locally. No history is stored, nothing is sent anywhere. Useful for quick cross-checks, copyright-year lookups, and schoolwork without surveillance.
Classical Roman numerals only go to 3999 (MMMCMXCIX). For larger numbers, Romans used a vinculum — a horizontal line over letters that multiplied their value by 1000. This tool supports vinculum notation for numbers up to 3,999,999, rendered using the Unicode combining overline character.
Standard Roman numeral rules forbid repeating a letter more than three times in a row; four would be written as IV (subtractive). Similarly V, L, and D can't repeat at all since their doubles have dedicated letters (VV=X, LL=C, DD=M). The tool validates these rules and flags violations.
Some clock faces use IIII instead of IV for visual symmetry with the VIII on the opposite side. That's a stylistic convention, not a valid Roman numeral. This tool enforces the classical rules.