Roman Numeral Converter

What Is a Roman Numeral?

Seven letters, fixed values, no place columns. Everything that makes Roman numerals easy to read aloud and awkward to compute with follows from that one design choice, and it is worth understanding before the rules make sense.

The Seven Letters and What They Are Worth

Wolfram MathWorld lists the set as the Latin letters I, V, X, L, C, D and M, standing for 1, 5, 10, 50, 100, 500 and 1,000. Nothing else counts: there is no eighth symbol, no digit for 2 or 7, and no letter above M in ordinary use.

Read the values in order — 1, 5, 10, 50, 100, 500, 1,000 — and they alternate. Each step multiplies the last by 5, then by 2, then by 5 again. That is why the system has a symbol for every power of ten and a halfway marker between each pair, and why the halfway markers (V, L, D) behave differently from the powers of ten (I, X, C, M) once the rules start.

The old mnemonic for the ladder still works: I Value Xylophones Like Cows Do Milk.

Additive, Not Positional — and Why That Means No Zero

In 2026 the leading 2 means two thousand purely because of the column it sits in. Move it and it means something else. In MMXXVI the two Ms mean two thousand because M is worth a thousand and there are two of them; slide them anywhere in the string and each one is still worth a thousand. Position carries value in one system and carries none in the other.

That single difference explains the missing zero. The MacTutor History of Mathematics archive separates zero's two jobs — an empty place indicator in a place-value system, and a number in its own right. A notation with no columns has no empty place to mark, so it never needed the first job at all. Roman numerals do not lack a zero symbol so much as they have nothing for one to do.

The cost is length. Because value is spelled out rather than positioned, numerals grow with the size of their parts: 3,888 needs fifteen characters (MMMDCCCLXXXVIII) while 2,000 needs two (MM).

The Six Subtractive Pairs

MathWorld states the rule plainly, in its own words: instead of using four symbols to represent a 4, 40, 9, 90 and so on, "such numbers are instead denoted by preceding the symbol for 5, 50, 10, 100, etc., with a symbol indicating subtraction." With only seven symbols to draw on, that gives exactly six legal pairs, and no others.

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

Only I, X and C ever go in front, and each one may only stand before the next two symbols up the ladder: I before V and X, X before L and C, C before D and M. V, L and D never subtract and never repeat, because each of them is already the halfway marker its own power of ten is built around — VV would just be X.

The pairs are not a rare special case. Of the 3,999 numerals this converter can produce, 1,952 contain at least one of them — a shade under half. The reason is arithmetic rather than taste: any 4 or 9 in the units, tens or hundreds place forces a pair, and 4,000 minus the 2,048 combinations that avoid a 4 and a 9 in all three places leaves exactly 1,952.

How Do You Convert Numbers to Roman Numerals?

One loop does the whole job. Take the largest value that still fits inside what is left, write its symbol down, subtract it, and go again until nothing remains.

The Rules, Written Out

Thirteen values sit in the table the converter walks: the seven letters plus the six subtractive pairs, ordered from largest to smallest. Greedy selection from that list produces the standard spelling of every number in range, with no backtracking and no special cases.

M  1000    CM 900    D  500    CD 400
C  100     XC 90     L  50     XL 40
X  10      IX 9      V  5      IV 4
I  1

2026  take M   -> 1026   write M
1026  take M   ->   26   write M
  26  take X   ->   16   write X
  16  take X   ->    6   write X
   6  take V   ->    1   write V
   1  take I   ->    0   write I
                        MMXXVI

Because 900 and 400 are in the table alongside 1,000 and 500, the greedy pass can never emit four identical symbols in a row. It reaches CM before it can reach a fourth C.

Step by Step With This Converter

• Leave Direction on Number → Roman. It is the left half of the two-way control and it is already selected when the page opens.
• Type a whole number from 1 to 3,999 into the Value box. Thousands commas are fine — 2,026 gives the same answer as 2026.
• Press Calculate. The page also runs itself once on load using the 2026 it starts with, so there is already an answer on screen before you touch anything.
• Read the numeral in the large readout, and the group-by-group build on the line underneath it.
• Reset clears the panel back to a dash, and Copy result puts the readout and its breakdown on the clipboard.

Nothing recalculates while you type. Editing the Value box leaves the previous answer on screen until you press Calculate again, which is worth knowing if you are working through a list of years.

Worked Example: 2026 Becomes MMXXVI

Two thousands, two tens, a five and a one. No subtractive pair is needed anywhere, because none of the digits is a 4 or a 9.

Top line of the result panel

MMXXVI

The line below it reads 2,026 = MM + XX + V + I, and a third line states that the numeral was built greedily from the largest values down. Change the year to 2024 and the build becomes 2,024 = MM + XX + IV, with the subtractive pair appearing the moment a 4 does.

A harder one to check by hand: 1999 returns MCMXCIX, and the panel breaks it out as 1,999 = M + CM + XC + IX. Three subtractive pairs in a single numeral, which is what makes that particular year notorious.

Reading a Numeral Back: MCMXCIX Returns 1,999

Switch Direction to Roman → Number and the scan runs left to right, one letter at a time. If a letter is worth less than the letter immediately after it, subtract it; otherwise add it. That single test handles both the ordinary runs and the subtractive pairs without treating them as separate cases.

M   1000 >= C     add 1000        running 1000
C    100 <  M     subtract 100    running  900
M   1000 >= X     add 1000        running 1900
X     10 <  C     subtract 10     running 1890
C    100 >= I     add 100         running 1990
I      1 <  X     subtract 1      running 1989
X     10 (last)   add 10          running 1999

Lowercase works too. Typing mcmxcix returns 1,999 and echoes the numeral back in capitals, so a numeral copied out of a footnote does not need tidying up first. Leading and trailing spaces are trimmed away as well.

The value comes back with a thousands separator — 1,999 rather than 1999 — because the readout formats numbers the way the rest of the site does.

Roman Numeral Chart: 1 to 3,999

Every numeral in the tables below came out of the converter on this page. Between them they cover the whole range, because a Roman numeral is just its digits' numerals written one after another.

The Seven Symbols, and What Each One May Do

M is the one row where the limit comes from the range rather than the rules. Three Ms is 3,000, and the converter stops at 3,999, so a fourth M never appears in anything it produces.

Roman Numerals 1 to 20

Exactly four of the twenty carry a subtractive pair: IV and IX, then XIV and XIX, which are the same two pairs with an X in front. The other sixteen are pure addition, and the second half of the row repeats the first — XI to XIII is X plus I to III, and XVI to XVIII is X plus VI to VIII.

Ones, Tens, Hundreds and Thousands

Read across a row to see the same digit at each scale the symbols allow. In the ones, tens and hundreds columns the pattern is identical: three repeats, then a subtractive pair at 4, the halfway symbol at 5, three more repeats, then a subtractive pair at 9. The thousands column stops after MMM, because there is no symbol above M for a 4,000 to subtract from and none to name a 5,000.

To write any number by hand, look up each of its digits in the right column and write the results in order. 1,776 is M for the 1, DCC for the 7, LXX for the second 7 and VI for the 6, giving MDCCLXXVI — exactly what the converter returns for 1776.

Years People Actually Look Up

The character column is the reason film credits changed shape at the turn of the century. Nineteen-hundreds years all start with the three-character MCM before they say anything specific; two-thousands years start with a two-character MM, so MMXXVI is six characters where MCMXCIX was seven for a smaller number.

How to Read Your Result

There are no bands, zones or categories here — a conversion is either right or wrong. What the panel does carry is a breakdown line that shows its working, and in one direction a note that appears only when your input is unusual.

The Number → Roman Panel

The large readout holds the numeral itself. Beneath it sits a line pairing the number you typed with its build, and beneath that a fixed sentence: Built greedily from the largest values down, with subtractive pairs (IV, IX, XL, XC, CD, CM) instead of four repeats.

The build groups by symbol value, not by decimal place, which is a genuine difference and occasionally a surprising one. Enter 1666 and the line reads 1,666 = M + D + C + L + X + V + I — all seven letters, once each, in descending order, the longest run of distinct symbols the system allows. Enter 3888 and it reads 3,888 = MMM + D + CCC + L + XXX + V + III.

So the groups do not line up with the digits of the number. For 1776 the panel shows 1,776 = M + D + CC + L + XX + V + I, splitting the 700 into D + CC rather than presenting DCC as one unit. Both readings describe the same numeral; the panel is showing which values the loop subtracted, in the order it subtracted them.

The Roman → Number Panel and Its Canonical-Form Note

Here the readout is the value, formatted with a thousands separator, and the line under it restates your numeral and what it reads as. A third line appears only when the spelling you typed is not the one the converter would have produced.

Type IIII and it returns 4, then adds: Note: the standard form of 4 is IV — the input reads fine but is not canonical. Type MIM and it returns 1,999 with the note naming MCMXCIX. Type XXXX and it returns 40 and names XL. The value is never withheld — the note is a correction of style, not a rejection.

No note means your numeral matched the standard spelling exactly. MCMXCIX, MMXXVI and MMMCMXCIX all come back with two lines and nothing else.

The Check Your Inputs Notice

Two messages exist, one per direction, and each one names the exact range or alphabet it wants.

• Number → Roman answers Enter a whole number from 1 to 3999 (standard numerals stop there) for 0, for 4000, for an empty box, and for letters typed into the number direction.
• Roman → Number answers Enter a Roman numeral using I, V, X, L, C, D, M whenever the box holds anything outside those seven letters — a digit, a space in the middle, a hyphen, or a single-character Ⅳ copied in from a word processor.

Both messages appear in the amber panel that replaces the readout, so a failed conversion never looks like an answer. If you see one unexpectedly, the usual cause is the Direction control still pointing the wrong way from your last conversion.

Where Roman Numerals Are Still Used

The system stopped being anyone's arithmetic centuries ago and survived as a marker — a way of signaling that a number names an edition, an installment or a monarch rather than counting anything.

Clock Faces, and the IIII Question

Roman dials are old enough that the convention predates any surviving explanation of itself. The Science Museum Group's record for the Wells Cathedral clock describes a weight-driven clock of 1392 whose beautifully decorated face is still in situ in the cathedral — among the oldest surviving clocks anywhere.

Many such dials print IIII at four o'clock rather than IV. Three explanations circulate: that the heavier IIII balances the VIII directly opposite it, that IIII and VI are harder to confuse at a distance than IV and VI, and that casting a dial needs only three molds if every numeral up to nine is additive. They are explanations in circulation rather than documented history, and no one of them settles it.

The converter takes the practical view. IIII returns 4 and VIIII returns 9, each with the canonical-form note attached, so you get the value and the standard spelling in the same answer.

Super Bowls, Film Credits and Monarchs

The NFL first used Roman numerals for Super Bowl V, the Baltimore Colts' win over the Dallas Cowboys in January 1971, and has kept to them since — Super Bowl LVIII is 58, Super Bowl LX is 60. The one deliberate break came at fifty: the league announced that it would be called Super Bowl 50, rather than Super Bowl L, then returned to Roman numerals for Super Bowl LI in February 2017.

Film and television credits are the other place almost everyone meets a numeral without looking for one. A copyright line reading MMXXVI is 2026; MCMLXXXVII is 1987. Elsewhere the pattern is ordinal rather than calendrical — Louis XIV, Elizabeth II, Super Bowl LX, Rocky IV, page xii of a preface, Article III of a constitution.

A birth year decoded from a plaque, a headstone or a flyleaf is usually only half of what you wanted. For the span between that year and today, use the Age Calculator.

Type Them as Ordinary Capital Letters

Unicode encodes single-character Roman numerals in the Number Forms block, U+2150 to U+218F. The Unicode Standard's own guidance is that for most purposes it is preferable to compose the Roman numerals from sequences of the appropriate Latin letters, and that the dedicated characters exist for compatibility with East Asian standards rather than as the recommended way to write them.

This converter follows that advice in both directions: it emits plain capital I, V, X, L, C, D and M, and it accepts only those seven letters going the other way. A numeral built from the compatibility characters is rejected rather than silently misread, which is the safer of the two failures.

Can You Do Math With Roman Numerals?

Not on this page. The tool converts between notations and does no arithmetic at all — there is one value box, not two, and no operator to choose. What it does give you is the fast route: read both numerals into numbers, do the sum however you normally would, and convert the answer back.

Adding and Subtracting: Convert, Compute, Convert Back

Three conversions and one piece of ordinary arithmetic in the middle. MDCCLXXVI plus CCL: the Roman → Number direction reads them as 1,776 and 250, the sum is 2,026, and Number → Roman turns that back into MMXXVI. Subtraction runs the same way — MMXXVI minus MDCCLXXVI is 2,026 − 1,776 = 250, which converts back to CCL.

The ceiling bites here more often than you would expect, because sums grow. MCMXCIX plus MMXXVI is 1,999 + 2,026 = 4,025, and that total has no standard numeral: the converter answers Enter a whole number from 1 to 3999 (standard numerals stop there). The two inputs were both perfectly legal and their sum is not writable.

Adding a span of years to a date, rather than adding two numerals together, is a different job and belongs to the Date Calculator.

Why Multiplication Is the Awkward One

Long multiplication depends on columns. You multiply digit by digit and shift the partial products left, and the shift is what does the work of multiplying by ten. Roman numerals have no columns to shift into, so that method has nothing to stand on.

Doubling still comes out cleanly, because doubling is just addition: MDCCLXXVI doubled is 3,552, which returns MMMDLII. Anything less tidy has to be rewritten as a sum, then re-encoded from scratch — which is exactly what the converter's greedy loop does, and it is doing it in decimal.

The honest summary is that the notation is for recording a number, not for working on one. Reading and writing it is quick; computing inside it is not, and there is no shortcut that avoids leaving the notation first.

Length Is Not Size

Two numerals cannot be compared by eye the way two decimal numbers can. MCMXCIX runs to seven characters and is worth 1,999. MM is two characters and is worth 2,000. The shorter numeral is the larger number, and neither the first letter nor the last gives it away.

The gap widens at the extremes. DCCCLXXXVIII is twelve characters for 888; MMM is three for 3,000. If you are sorting a list of numerals — chapter headings, edition numbers, a run of copyright years — convert them all first. Sorting the strings themselves puts MMM ahead of MMXXVI — 3,000 filed before 2,026 — because the two agree on MM and then the alphabet ranks M ahead of X.

Limits: Where This Converter Stops

The tool does one thing in two directions, and the two directions do not have the same edges. That asymmetry is the part worth reading before you trust an unusual answer.

• Number → Roman stops at 3,999. Enter 4000 and you get the amber notice, not MMMM, because MMMCMXCIX is the largest numeral standard notation reaches. Beyond it the Romans used a vinculum — MathWorld describes it as an overline placed on a numeral to indicate multiplication by 1,000 — and this converter neither prints one nor reads one.
• Roman → Number does not stop at 3,999. MMMM returns 4,000 and MMMMM returns 5,000, both with no canonical-form note, because a greedy re-encode of those totals produces the same strings. A value above the ceiling therefore converts one way and refuses to convert back.
• There is no zero and no negative. Entering 0 returns the amber notice. A minus sign is stripped rather than refused, so -5 comes back as V — check the sign yourself before quoting an answer.
• There are no decimals or fractions. The Value box discards every character that is not a digit, which is what makes 2,026 work, and also means 12.7 is read as the whole number 127 and returns CXXVII. Enter whole numbers only.
• Roman → Number checks the alphabet, not the grammar. Anything built from the seven letters is scanned by the same add-or-subtract rule, so IIIIIIIIII returns 10, IVIV returns 8 and VX returns 5, each flagged as non-canonical rather than rejected. A malformed numeral gets a reading, not an error.
• The panel holds one conversion. Direction is a two-way segmented control and Value is the only box — no second value, no operator and no memory between runs — so a multi-step problem has to be carried across by hand.
• Nothing recomputes until you press Calculate. An edited Value box sits next to the previous answer until then, which matters most when you are working quickly through a column of years.

None of this is a flaw in the numerals themselves. A notation designed to be carved, read across a plaza and understood without a symbol for nothing was never going to survive contact with decimals, and the places it still lives — dials, credits, regnal names — are precisely the ones where none of that is asked of it.