Roman Numerals: Rules, Chart, and Common Mistakes

Every February the Super Bowl logo reminds a few million people that they’ve forgotten how Roman numerals work. LVIII, LIX, LX — the letters keep marching on, and somewhere a group chat is arguing about what they add up to. (LVIII is 58, for the record.)

Roman numerals are one of those systems everyone half-knows. You can read a clock, probably a film’s copyright year, but ask someone to write 1989 off the top of their head and watch them stall. Here’s how the whole thing works, and where it trips people up.

Seven letters, and that’s the entire alphabet

The system runs on seven symbols:

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

Everything else is those letters stacked and added together. MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1 = 2026. You read left to right, largest to smallest, and sum as you go.

The subtractive rule, where it gets slippery

There’s one twist. To avoid writing four of the same letter in a row, a smaller symbol placed before a larger one gets subtracted:

IV = 4 (not IIII)
IX = 9
XL = 40
XC = 90
CD = 400
CM = 900

So 1999 isn’t MIM or some improvised shorthand — it’s MCMXCIX: M (1000) + CM (900) + XC (90) + IX (9). Four subtractive pairs in a single number, which is exactly why people get it wrong. Type 1999 into the Roman Numeral Converter and it shows MCMXCIX with each piece split out.

Writing any number: split it by place

The trick nobody teaches is that you never convert a number as a whole. Break it into thousands, hundreds, tens and units, do each part on its own, then write the four pieces left to right. 1984:

1000 → M
900 → CM
80 → LXXX
4 → IV

Stick them together and you have MCMLXXXIV. The converter prints exactly this split under every result, which is also the fastest way to check one you wrote by hand: if the pieces come out in descending order of size, the numeral is well-formed.

Going the other way is the same idea in reverse. Read left to right, and whenever a letter is smaller than the one after it, subtract instead of adding.

The IIII on your clock isn’t a bug

Here’s a fun contradiction. The rules say 4 is IV, and the converter rejects IIII as invalid. Yet look at a traditional clock face and you’ll almost always find IIII at the four o’clock mark, not IV. Clockmakers have done this for centuries — partly for visual balance against the VIII across from it, partly just habit. So the “wrong” form is the standard one on clocks, and the “right” form is everywhere else.

What the system can’t do

Two limits are worth knowing:

There’s no zero. The Romans had no symbol for it. When they needed to write “none,” they used the word nulla. That’s why the smallest numeral is I.
It stops at 3999 (MMMCMXCIX). No single letter is worth more than 1000, and stacking four M’s would break the no-four-in-a-row habit. For bigger numbers, scribes drew a bar over a letter to multiply it by 1000, but you rarely need that now.

Dates: three numerals, not one

Engravings, cornerstones and jewellery write dates in Roman numerals, and this is where most mistakes happen — because a date is not one number. The day, the month number and the year convert separately and then get joined:

4 July 1976 → IV · VII · MCMLXXVI

Keep the separator. Run the three together and IVVIIMCMLXXVI is genuinely unreadable: nothing marks where the day ends and the month starts, so several different dates produce the same string. A dot, a middle dot or a slash all work; engravers usually pick the middle dot. There’s a month table and a worked example on the converter page.

Forms that look right and aren’t

Four rules cover nearly every bad numeral:

No four in a row. IIII is 4 written the old way, XXXX is 40 — the modern forms are IV and XL.
Subtraction skips one step only. I may stand before V or X, X before L or C, C before D or M. That’s it. So 99 is XCIX, not IC, and 49 is XLIX, not IL.
Only I, X and C subtract. V, L and D never go in front of a bigger letter, which rules out VX and LC.
Descending order otherwise. MIM has a subtractive pair that doesn’t exist, so it means nothing. 1999 is MCMXCIX.

The converter flags all four rather than guessing, on the grounds that a silent “best guess” is how a wrong year ends up carved into something permanent.

Where you’ll actually use them

Reading them comes up more than writing them: chapter and volume numbers, Olympic games, monarch names like Elizabeth II and Louis XIV, cornerstones on old buildings, and the copyright year buried in film credits that flashes past too fast to decode. Being able to convert one on the spot saves a lot of squinting.

Paste a year, a chapter number, or a numeral you can’t parse into the Roman Numeral Converter — it works both directions, instantly, and the full 1–100 chart and every year to 2030 sit right underneath it.