Roman Numeral Converter

Convert Roman numerals in either direction

Type a number to see its Roman numeral, or type a numeral to see its number. Both boxes stay live, so whichever one you edit becomes the source and the other follows. The conversion runs in your browser; the only place a value is kept is in the page address, and only so you can share a particular conversion.

The seven letters

Roman numerals are built from seven letters, each with a fixed value:

I = 1 · V = 5 · X = 10 · L = 50 · C = 100 · D = 500 · M = 1000

A numeral is read from left to right, adding as you go. XVI is 10 + 5 + 1 = 16. Letters are written in descending order of value, and no letter is repeated more than three times in a row.

Subtractive pairs

When a smaller letter sits immediately before a larger one, it is subtracted rather than added. This is what avoids IIII and VIIII:

IV = 4 · IX = 9 · XL = 40 · XC = 90 · CD = 400 · CM = 900

Only these six pairs are valid. A letter may only be subtracted from the next two values up its own scale — I from V and X, X from L and C, C from D and M — which is why IL, IC and VX are not numerals at all, even though their intent is guessable. MCMXCIX is 1000 + 900 + 90 + 9 = 1999, and reading it means handling three subtractive pairs in a row.

Why the range stops at 3999

M is the largest symbol, and the no-more-than-three-repeats rule caps the thousands at MMM. That makes MMMCMXCIX — 3999 — the largest value standard notation can express.

Larger numbers were written with a vinculum, a bar drawn over a letter to multiply it by a thousand, so a barred V meant 5000. There is no agreed way to type that as plain text: writing it as |V|, V̄ or (V) produces something most other tools would not read back correctly. This converter reports the limit rather than inventing a spelling.

Strict spelling, and why

You will see IIII on clock faces, on cornerstones, and in plenty of historical inscriptions. It is genuine, but it is not modern standard notation, which writes 4 as IV.

This converter accepts only the standard spelling of each value. That is a deliberate trade: a converter that quietly accepted every variant could never tell you that you had mistyped something. Because there is exactly one correct way to write each number, the tool can check your numeral by converting the value back and comparing — so IIII, MMMM and IXI are all reported as errors rather than silently interpreted.

Common numerals at a glance

1–10: I, II, III, IV, V, VI, VII, VIII, IX, X

Tens: X = 10, XX = 20, XXX = 30, XL = 40, L = 50, LX = 60, LXX = 70, LXXX = 80, XC = 90, C = 100

Recent years: MM = 2000, MMX = 2010, MMXX = 2020, MMXXVI = 2026

Where you still meet them

Roman numerals survive where a number needs to look formal or to sit apart from ordinary figures: monarchs and popes, Super Bowls, film copyright dates, book prefaces numbered separately from the main text, clock faces, and the outlines of legal documents. They are almost never used for arithmetic, which is exactly what they are bad at — the system has no zero, no place value, and no way to write a fraction or a negative number.

Frequently asked questions

How do Roman numerals work?

Seven letters carry values — I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000 — and a numeral is read by adding them from left to right. When a smaller letter appears before a larger one it is subtracted instead: IV is 4 and IX is 9. Only six subtractive pairs are allowed: IV, IX, XL, XC, CD and CM.

Why does the converter stop at 3999?

M is the largest single symbol, and standard numerals never repeat a symbol more than three times, so MMMCMXCIX (3999) is the largest value that can be written. Higher numbers need a vinculum — a bar over a letter meaning multiply by a thousand — which has no agreed way of being typed as plain text. Rather than invent a spelling no other tool would read back, the converter says so.

Why is IIII rejected when clocks use it?

IIII appears on clock faces and some monuments, but modern standard notation writes 4 as IV. This converter is strict so it can tell you when a numeral is mistyped — accepting every historical variant would mean never being able to flag a genuine error. The same rule rejects IM, VX and other spellings you may occasionally see.

Is there a Roman numeral for zero?

No. The system has no symbol for zero and no way to write a negative number; it was built for counting and recording quantities, not for arithmetic. The idea of zero as a number in its own right reached Europe centuries later, with the Hindu-Arabic digits that replaced numerals for calculation.

How do I write the current year?

2026 is MMXXVI: two thousands (MM), two tens (XX), a five (V) and a one (I). Type any year into the number box to see it converted.

Does capitalization matter?

Not for reading. The converter accepts lowercase and mixed case and ignores spaces around what you type, then shows the numeral back in the conventional uppercase form.