Roman numeral converter

How do I write 2026 in Roman numerals?

MMXXVI: MM = 2,000, XX = 20, VI = 6. Break the number into thousands, hundreds, tens and ones and write each part.

How do I read Roman numerals?

Add the values left to right — I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1,000 — but subtract a smaller one that comes before a larger one. MCMXCIV = 1,000 + 900 + 90 + 4 = 1994.

Which subtractions are allowed?

Only six: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). So 99 is XCIX, not IC, and 8 is VIII, not IIX.

What is the largest Roman numeral?

With the standard symbols, 3,999 — MMMCMXCIX. Larger numbers used a bar over a letter to multiply it by 1,000, which is not standard today.

Why do some clocks show IIII instead of IV?

Tradition: many clock makers use IIII for 4 for visual balance with VIII on the other side. In ordinary writing, 4 is IV. There is also no Roman numeral for zero.

Why is 49 written XLIX and not IL?

Subtraction is only allowed for I before V and X, X before L and C, and C before D and M, and only one subtracted symbol at a time. So 49 is built from 40 (XL) and 9 (IX): XLIX.

How the conversion works

To write a number, take its digits from the thousands down. Each digit has a fixed pattern: for the ones, 1 to 9 is I, II, III, IV, V, VI, VII, VIII, IX; the tens use X, L and C in the same pattern; the hundreds use C, D and M; and the thousands are written with M. To read a number, scan from the left and add each value, except that a symbol smaller than the one after it is subtracted. The rules also forbid repeating V, L or D, and I, X, C or M may appear at most three times in a row.

Worked examples

The calculator gives 49 = XLIX, 444 = CDXLIV, 1994 = MCMXCIV, 2026 = MMXXVI, 3999 = MMMCMXCIX. Take 1994: one thousand is M, nine hundred is CM, ninety is XC and four is IV, so MCMXCIV. To read XLIX, X before L is 40 and I before X is 9, which makes 49. Strings that break the rules are not accepted: IIII (rejected), IC (rejected), VX (rejected). The largest value is 3,999, since writing 4,000 would need four Ms in a row.

Common mistakes

Writing a shortcut subtraction such as IC for 99 or VL for 45 is the most common error; 99 is XCIX and 45 is XLV. Another is subtracting more than one symbol, as in IIX for 8, which is VIII. Reading from the right instead of the left also gives wrong totals. Lastly, there is no symbol for zero, and the Roman system has no place value, which is why it is awkward for arithmetic and why dates and chapter numbers are its main use today.

Sources: the standard modern rules for forming Roman numerals (these are conventions rather than an official standard; historical usage varied, for instance IIII on clock faces). Related: number to words converter, base converter, binary converter and hex calculator.