Both directions, up to 3,999,999. Type a number or paste a numeral — the converter works out which way you are going.
Range 1 to 3,999,999. Type a whole number to get the numeral, or paste a numeral (I V X L C D M) to read its value. No zero, no negatives, no decimals.
Type a number — the current year, for instance — and read the numeral straight away.
Copied
01 · the seven letters
I
1
V
5
X
10
L
50
C
100
D
500
M
1,000
Written largest to smallest and added: MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1, which is 2026. Almost every numeral you meet works exactly that way, read left to right like a running total.
The exception is what makes the system interesting, and it is the only rule that needs learning.
02 · the rules
▸ Additive by default
Letters are written largest to smallest and added up: MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1.
▸ Subtractive for four and nine
A smaller letter before a larger one is subtracted: IV is 4, IX is 9, XL is 40, CM is 900.
▸ Only one step down
You may subtract I from V or X, X from L or C, and C from D or M. Never IL for 49 or IC for 99 — those step two orders and are not valid.
▸ No more than three in a row
III is fine, IIII is not, which is why 4 is IV. The same limit gives XXX, CCC and MMM as the maximum runs.
▸ No zero, no negatives, no fractions
The system has no symbol for nothing and no way to write half of anything. It was built for counting, not arithmetic.
The third rule is the one people get wrong. Subtraction steps down exactly one order, so 49 is XLIX rather than IL, and 99 is XCIX rather than IC. Both of the shorter forms are readable and neither is valid, which the converter will tell you if you paste one in.
03 · worked examples
| Number | Numeral | How |
|---|---|---|
| 4 | IV | Subtractive: one before five. |
| 9 | IX | One before ten, not VIIII. |
| 14 | XIV | Ten, then four. |
| 40 | XL | Ten before fifty. |
| 49 | XLIX | Not IL — subtraction only steps down one order. |
| 1492 | MCDXCII | M, CD, XC, II. |
| 2026 | MMXXVI | The current year. |
| 3999 | MMMCMXCIX | The largest without an overline. |
04 · the clock
Look at a traditional clock face and the four is almost always IIII, not IV — on a system where IIII is supposed to be wrong. It is the most visible exception to the rule anywhere, and it is genuinely unexplained.
The explanations offered are many and none is settled. Visual balance is the most convincing: IIII on the left side of the dial answers the weight of VIII on the right, and a face with the lighter IV looks unbalanced. Others point to casting — a set of numerals for a dial divides neatly into moulds if you use IIII — or to the difficulty of reading IV upside down at that angle.
Whatever the reason, the convention is old, near-universal, and worth knowing before you conclude a clockmaker made a mistake. This converter follows the standard rule and returns IV; the clocks are the exception, not the system.
05 · past 3,999
M cannot repeat more than three times, so the largest numeral in the plain system is MMMCMXCIX, 3,999. That was enough for most Roman purposes and not for all of them, so a notation existed for going further: a bar drawn over a numeral — the vinculum — multiplies it by a thousand.
With it, V with a bar is five thousand and X with a bar is ten thousand, which extends the range to 3,999,999 before the same repetition limit bites again. The converter above uses the vinculum automatically once a number passes 3,999, and says so beneath the result.
In practice you will almost never meet one. Numbers that large stopped being written in Roman numerals long before anybody needed to render them on a screen, and the notation survives mainly in transcriptions of inscriptions and in converters like this one.
06 · where they survive
Roman numerals lost the argument with Arabic ones around the thirteenth century, for a reason that is easy to miss: they are perfectly good for recording a quantity and nearly useless for calculating with one. There is no column to carry into, no zero to hold a place, and no way to line two numbers up and add them. Anyone who has tried multiplying MMXXVI by XIV understands why the change stuck.
What they kept is everything where the number is a label rather than a quantity. Monarchs and popes take them — Elizabeth II, Benedict XVI — and so do book chapters, prefaces numbered separately from the main text, the outline levels of a formal document, Super Bowls, and the copyright date at the end of a film. In each case nobody is going to add the numbers up; they are being named, or ranked, or made to look permanent.
The clock face belongs in that list too, and it is the only place most people meet a Roman numeral daily. It is also the place where the system breaks its own rule, which says something about how much of this is convention rather than arithmetic.
One practical note for anyone writing them: the numerals are letters, not symbols, so they are typed as ordinary capitals and inherit whatever font the surrounding text uses. A numeral set in a font with old-style figures will look wrong beside them, and small caps are a common typographic choice for exactly that reason.
07 · questions
Q01
Seven letters carry fixed values — I, V, X, L, C, D, M — and are written largest to smallest, adding as they go. The one exception is subtraction: a smaller letter placed before a larger one is taken away, which is how 4 becomes IV and 900 becomes CM.
Q02
Because no letter repeats more than three times in the standard system, so IIII gives way to IV. That said, IIII was common historically and still appears in one very visible place — see the clock question below.
Q03
Nobody knows for certain, and there are several explanations. The most practical is visual balance: IIII on the left mirrors the weight of VIII on the right, and a face with IV looks lopsided. Whatever the reason, the convention is old and near-universal on traditional dials — a clock with IV is the unusual one.
Q04
Without extra notation, 3,999 — MMMCMXCIX — because M cannot repeat more than three times. Past that the Romans used an overline, the vinculum, which multiplies the letters beneath it by a thousand, taking the range to 3,999,999. This converter supports both.
Q05
No. The system has no zero, which is one reason arithmetic with it is so awkward — there is no place-value column to leave empty. Medieval scholars occasionally wrote "N" for nulla when a zero was needed, but it was never part of the numeral system proper.
Q06
Subtraction only steps down one order at a time: I may go before V or X, X before L or C, C before D or M. IL would be subtracting one from fifty, two orders apart, which the system does not allow. So 49 is built as XL (40) plus IX (9).
Q07
Clock faces, book chapters and prefaces, monarch and pope names, film copyright dates, Super Bowls, and the outline levels of formal documents. In almost all of them the point is the look rather than the arithmetic — nobody adds up in Roman numerals.
Q08
The numerals themselves do not — MMXXVI is MMXXVI everywhere, which makes this the one tool on this site whose algorithm is genuinely shared across the three languages. What differs is how they are read aloud: English says "the Second" for II in a name, Spanish "segundo", Portuguese "segundo".
Those two rules build every numeral you will meet. The converter works in both directions and will tell you when a numeral is readable but not canonical.