Roman Numeral Converter
Convert a decimal number (1-3999) to a canonical Roman numeral, or a canonical Roman numeral back to decimal.
Calculator Inputs
Decimal must be an integer from 1 to 3999. Roman numerals must be canonical (e.g. "IV", not "IIII"). Date mode takes a modern calendar date as YYYY-MM-DD (year 1-3999) and writes its month, day and year in Roman numerals; it is not an ancient Roman calendar conversion.
- Roman numeral
- MCMXCIV
- Decimal
- 1,994
About these results
CalcSpectrum calculators produce automated estimates using established formulas and the specific values you enter. Because real-world outcomes depend on input accuracy, mathematical assumptions, and rounding conventions, please verify critical figures with an appropriately qualified financial, tax, medical, legal, or other professional, as relevant.
How It's Calculated
Formula
Roman numerals combine seven symbols (I=1, V=5, X=10, L=50, C=100, D=500, M=1000) by repetition and subtraction to represent whole numbers from 1 to 3999. This converter produces the canonical form — the single standard way to write each number, using the standard subtractive pairs (IV, IX, XL, XC, CD, CM) instead of four repeated symbols. Converting from Roman to decimal only accepts canonical input: non-standard forms like "IIII" (instead of "IV") or invalid subtractive pairs like "IL" or "IC" are rejected rather than silently reinterpreted.
Worked Examples
Convert 1994 to Roman numerals
- 1994 = 1000 + 900 + 90 + 4.
- 1000 -> M, 900 -> CM, 90 -> XC, 4 -> IV.
- Result: MCMXCIV.
Convert MMXXIV to decimal
- MM = 1000 + 1000 = 2000.
- XX = 10 + 10 = 20.
- IV = 4.
- Result: 2000 + 20 + 4 = 2024.
Frequently Asked Questions
Why is "IIII" rejected instead of converted to 4?
"IIII" is not the canonical Roman numeral for 4 — the standard form is "IV" (subtractive notation). This converter rejects non-canonical input rather than guessing what you meant.
What is the supported range?
1 to 3999. Standard Roman numeral notation has no single-character symbol for 0, and no standard way to write 4000 or higher without non-standard extensions.
Is lowercase Roman numeral input accepted?
Yes. Lowercase input is normalized to uppercase before validation, so "mcmxciv" is accepted the same as "MCMXCIV".