Roman Numeral Calculator
Convert numbers and Roman numerals, check whether a numeral is written in standard form, calculate with two values, or write a calendar date in Roman numerals.
How this Roman numeral calculator works
Modern Roman numerals normally write values from largest to smallest. The six conventional subtractive pairs are IV, IX, XL, XC, CD and CM. This calculator uses the common modern form for the integers 1 through 3,999. It does not guess at nonstandard spellings: for example, 49 is XLIX, not IL.
| Roman symbol | Value | Example |
|---|---|---|
| I | 1 | III = 3 |
| V | 5 | VIII = 8 |
| X | 10 | XIV = 14 |
| L | 50 | XL = 40 |
| C | 100 | XC = 90 |
| D | 500 | CD = 400 |
| M | 1,000 | MMXXVI = 2,026 |
Checked examples
| Input | Calculation | Result |
|---|---|---|
| 1,984 | 1,000 + 900 + 80 + 4 | MCMLXXXIV |
| MMXXVI | 2,000 + 20 + 6 | 2,026 |
| XIV + VI | 14 + 6 | XX = 20 |
| 12/31/2026 | XII / XXXI / MMXXVI | XII/XXXI/MMXXVI |
| 3,999 | 3,000 + 900 + 90 + 9 | MMMCMXCIX |
Formula and validation rules
To create a Roman numeral, the calculator repeatedly removes the largest value available from this ordered list: 1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4 and 1. To read a numeral, it totals the same symbols and subtractive pairs, then converts the total back to Roman form. If the reconstructed form does not exactly match the cleaned input, the input is rejected as nonstandard.
- Only positive whole numbers from 1 through 3,999 use the supported standard notation.
- Zero, negative values, decimals, fractions and results above 3,999 have no output in this calculator.
- Overlines, parentheses and medieval variants for values above 3,999 are not accepted because their conventions are not uniform.
- Arithmetic is performed with Arabic-number values, then the valid integer result is converted back to Roman form.
- The date tool checks the real number of days in the selected month, including Gregorian leap years.
Frequently asked questions
Can I enter lowercase Roman numerals?
Yes. Lowercase input is converted to uppercase, and ordinary spaces are ignored.
Why is IIII rejected?
Some clocks and historical inscriptions use IIII, but the conventional modern form of 4 is IV. Strict validation prevents multiple spellings from being treated as equivalent.
How do I write zero in Roman numerals?
The classical system has no standard symbol for zero, so this calculator does not create one.
Can Roman numerals represent numbers above 3,999?
Extended systems exist, often using overlines or parentheses, but they are not consistently encoded or displayed. The calculator deliberately stops at the unambiguous modern range.
Related calculators
Use the Long Division Calculator for quotients, remainders and steps, the Exponent Calculator for powers and roots, or the Date Calculator to add, subtract and compare calendar dates.