The Seven Symbols
| Symbol | Value | Origin |
|---|---|---|
| I | 1 | A single tally mark |
| V | 5 | An open hand, five fingers |
| X | 10 | Two hands, or a crossed tally |
| L | 50 | From a Chalcidic Greek letter |
| C | 100 | Latin centum |
| D | 500 | Half of the old symbol for 1,000 |
| M | 1,000 | Latin mille |
The Rules
- Addition. Symbols are written from largest to smallest and added: XVI = 10 + 5 + 1 = 16.
- Subtraction. A smaller symbol before a larger one is subtracted: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900.
- Only six subtractive pairs exist: IV, IX, XL, XC, CD, CM. Nothing else is valid — IC for 99 and IL for 49 are wrong, however logical they look. 99 is XCIX.
- Only I, X and C subtract. V, L and D never appear before a larger symbol.
- Maximum three repeats. III is valid, IIII is not. V, L and D never repeat at all.
This calculator enforces every rule by converting the number and checking the result matches your input exactly, so invalid forms are rejected rather than silently accepted.
Common Numbers
| Number | Roman | Number | Roman |
|---|---|---|---|
| 1 | I | 40 | XL |
| 2 | II | 50 | L |
| 3 | III | 60 | LX |
| 4 | IV | 90 | XC |
| 5 | V | 100 | C |
| 6 | VI | 400 | CD |
| 7 | VII | 500 | D |
| 8 | VIII | 900 | CM |
| 9 | IX | 1,000 | M |
| 10 | X | 1,500 | MD |
| 14 | XIV | 1,900 | MCM |
| 19 | XIX | 1,994 | MCMXCIV |
| 20 | XX | 2,026 | MMXXVI |
| 30 | XXX | 3,999 | MMMCMXCIX |
Why the Limit Is 3,999
Since M is the largest symbol and no symbol may repeat more than three times, the largest writable number is MMMCMXCIX = 3,999. The Romans handled larger values with the vinculum — a bar over a numeral multiplying it by 1,000, so V meant 5,000 — but there is no standard modern typography for it, and it is not used in practice.
There Is No Zero
Roman numerals have no symbol for zero, and no way to write negative numbers or fractions in the ordinary system. This is not an oversight: the system is a tally notation for counting and recording, not a positional system for calculating. Multiplication and division in Roman numerals are close to impossible, which is why merchants used an abacus and why the arrival of Hindu-Arabic numerals in Europe was transformative.
Fractions were handled separately in twelfths, with their own symbols: uncia for 1/12, semis (S) for 1/2.
Where They Are Still Used
- Clock faces — often with IIII rather than IV, a long-standing horological convention that balances the dial visually against the VIII opposite.
- Film and television copyright dates, historically to make a production's age less obvious at a glance.
- Monarchs and popes — Elizabeth II, Louis XIV, Benedict XVI.
- Super Bowls, every year except Super Bowl 50, where L was judged to look wrong on its own.
- Book prefaces, numbered i, ii, iii before the main pagination begins.
- Building cornerstones and monuments.
- Chemistry and medicine — oxidation states, cranial nerves, cancer stages.
Reading Long Numerals
Work from the left in place-value groups — thousands, hundreds, tens, units — rather than symbol by symbol. MCMXCIV splits as M (1000) + CM (900) + XC (90) + IV (4) = 1994. Reading it as M-C-M-X-C-I-V invites mistakes; reading it in groups does not.
Frequently Asked Questions
Why is 4 sometimes IIII on clocks?
Tradition and symmetry. IIII balances the VIII directly opposite it on the dial, and it also lets a clockmaker cast the numerals in three moulds. Big Ben is a notable exception, using IV.
Is IC valid for 99?
No. Only I, X and C may be subtracted, and only from the next two higher symbols. 99 is XCIX — ninety (XC) plus nine (IX).
How do I write the current year?
2026 is MMXXVI: two thousands, two tens, a five and a one.
What is the largest Roman numeral?
MMMCMXCIX, or 3,999, in the standard system. Larger values require the overline notation, which has no common modern form.