Type a number or a Roman numeral to convert instantly — then try the quiz below.
Converter
Quiz — 10 questions
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How Roman numerals work
Seven letters carry all the values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Values add from left to right (VIII = 8), but a smaller value before a larger one subtracts (IV = 4, IX = 9, XL = 40, CM = 900) — only I, X and C can be used that way. Numerals still appear on clock faces, book chapters, movie sequels and events like Super Bowl LVIII, so reading them fluently is a small skill that keeps paying off. The quiz mixes both directions and gets you fluent fast.
The seven letters and two rules
Seven letters carry every value: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. Values are written largest first and added together, so MMXXIV reads as 1000 plus 1000 plus 10 plus 10 plus 4.
The exception is subtraction: a smaller value placed before a larger one is taken away instead. IV is 4, IX is 9, XL is 40, XC is 90, CD is 400 and CM is 900. Only I, X and C are ever used this way, and only before the next two values up — which is why 99 is XCIX and never IC.
Two more constraints finish the system. The same letter never repeats more than three times in a row, which is why 4 is IV rather than IIII. And V, L and D are never repeated at all, since two of any of them would simply be the next letter up.
Converting in your head
Going from a number, break it into thousands, hundreds, tens and units and convert each separately. 1984 becomes M, CM, LXXX, IV — written straight through as MCMLXXXIV.
Going from letters, read left to right and add — but check each letter against the one after it first, and subtract if it is smaller.
Memorise the tens: X, XX, XXX, XL, L, LX, LXX, LXXX, XC. Everything between 1 and 99 comes from these plus the units.
A useful sanity check: if a smaller letter appears before a larger one more than once in a row, the numeral is malformed.
There is no zero and no way to write a negative number or a fraction of one — a genuine limitation of the system, not an omission here.
Where you still meet them
Roman numerals stopped being used for calculation centuries ago, but they survive wherever a number needs to look formal or needs to be distinguished from an ordinary count. Clock faces, book chapters and preface page numbers, monarch and pope names, film copyright dates, building cornerstones, and the Super Bowl all still use them.
Clock faces are the one place where the rules are routinely broken. Many traditional dials write four as IIII rather than IV, a convention that predates the standardisation of the subtractive rule and gives the face better visual balance against the VIII opposite it.
Standard Roman numerals repeat a letter at most three times, so MMMCMXCIX (3999) is the largest normal form. The Romans wrote bigger numbers with a bar over letters (V̄ = 5000), but that notation isn't standard today.
Why is 4 written IV and not IIII?
Subtractive notation (IV = 5−1) became the standard because it's shorter. Fun exception: many clock faces still use IIII for visual balance with VIII on the opposite side of the dial.
Is there a Roman numeral for zero?
No — the classical system has no symbol for zero, since it counts things rather than positions. Medieval scholars later used the word "nulla" (or the letter N) in tables, but it was never part of standard Roman notation.
Why is 99 written XCIX and not IC?
The subtraction rule only allows six pairs: IV, IX, XL, XC, CD, CM — you can only subtract I, X or C from the next two steps up. So 99 = XC (90) + IX (9), and 1999 is MCMXCIX rather than MIM.
Why do movies, kings and the Super Bowl use Roman numerals?
Tradition and gravitas: monarchs and popes have been numbered that way for centuries (Elizabeth II, Louis XIV), film credits adopted them for copyright years, and the Super Bowl uses them (LVIII = 58) so each edition reads as a grand title rather than a plain number.