tigtools

Roman Numeral Converter

Type a number to get its Roman numeral, or type a Roman numeral to get its value. Non-standard forms are flagged with the reason and the correct spelling.

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Number to Roman numeral

MMXXVI

MM (2,000) + XX (20) + V (5) + I (1)

Roman numeral to number

Standard form: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Symbols go from largest to smallest; IV, IX, XL, XC, CD and CM are the only subtractive pairs.

How to use it

  1. To convert a number, type a whole number from 1 to 3999 in the left field.
  2. Read the Roman numeral and the breakdown of its parts, for example M (1000) + CM (900) + XC (90) + IV (4).
  3. To convert the other way, type a Roman numeral in the right field. Upper or lower case both work.
  4. If the numeral is not in standard form, read the explanation and use the suggested spelling.

How it works

Modern Roman numerals use seven symbols: I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). A number is written from the largest symbol to the smallest, and the values are added: MDCLXVI = 1000 + 500 + 100 + 50 + 10 + 5 + 1 = 1666.

To avoid four identical symbols in a row, six subtractive pairs are used: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). Only I, X and C are ever subtracted, and only from the next two larger symbols. V, L and D are never repeated.

The converter accepts a Roman numeral only if it is exactly the standard spelling of its value. Forms such as IIII (seen on clock faces), VX or IC were used historically or appear in puzzles, but they are not standard; the tool explains which rule is broken and shows the standard form of the value they would loosely mean.

The standard system covers 1 to 3999. There is no zero, no negative numbers and no fractions. Larger numbers were written with a bar (vinculum) or other conventions that were never standardised, so they are not supported.

Examples

A year

1994 = M (1000) + CM (900) + XC (90) + IV (4) = MCMXCIV. 2026 = MMXXVI.

Clock face IIII

IIII is rejected: I may not appear four times in a row. Read loosely it means 4, which is written IV.

A wrong subtraction

IC is not 99, because I may only be subtracted from V and X. 99 is XC (90) + IX (9) = XCIX.

Frequently asked questions

What is the largest Roman numeral?

In standard form, 3999 = MMMCMXCIX. Writing 4000 would need four M's in a row or a special notation such as a bar over the numeral, which is not standardised.

Why do some clocks show IIII instead of IV?

It is a design tradition, often explained by visual balance with VIII on the other side. IIII is not the standard spelling of 4.

Is there a Roman numeral for zero?

No. The Roman system had no symbol for zero. Medieval texts sometimes used the word nulla or the letter N, but that is not part of the numeral system.

Is lower case allowed?

Yes. Input is converted to upper case before it is checked, so mcmxciv gives 1994.

Privacy

The conversion runs in your browser. What you type is not sent or stored.