Roman Numeral Converter

Roman numerals are everywhere once you start looking: the copyright year at the end of a film (MMXXVI for 2026), Super Bowl titles, the chapters of a book, monument inscriptions, clock faces, and the suffixes after a name like Henry VIII. This Roman numeral converter turns any whole number from 1 to 3999 into its Roman form and decodes Roman numerals back into ordinary numbers - and just as importantly, it shows you the math so you can read and write them yourself.

For example, the number 2026 becomes MMXXVI. The converter builds that by taking the largest pieces it can: 1000 + 1000 (MM) for 2000, 10 + 10 (XX) for 20, and 5 + 1 (VI) for 6. Read the result left to right, largest values first, and you get the year exactly as you would see it on a film's end credits.

The seven Roman numeral symbols

Every Roman numeral is built from just seven letters. Memorizing their values is the whole game:

A handy mnemonic for the order M, D, C, L, X, V, I is "My Dear Cat Loves Xtra Vitamins Intensely." Once you know the letters, the rest is just two rules: when to add and when to subtract.

The two rules: adding and subtracting

Rule 1 - Add when going down. When symbols are written in order from larger to smaller, you add them. So VIII is 5 + 1 + 1 + 1 = 8, and CLX is 100 + 50 + 10 = 160. This is the default behavior, and most of a numeral works this way.

Rule 2 - Subtract when a smaller symbol comes first. When exactly one smaller symbol sits immediately before a larger one, you subtract it. There are only six legal subtractive pairs:

That is the entire system. Combine the additive default with these six subtractive shortcuts and you can write or read any number up to 3999.

Symbol reference table

This table shows every symbol and subtractive pair, with a small example of each in use:

How to use this converter

The tool has two tabs, so you can go in either direction:

1. Number → Roman: select the first tab and type a whole number from 1 to 3999. The Roman numeral appears instantly, along with a table showing which symbol value contributes what.
2. Roman → Number: select the second tab and type a Roman numeral (upper or lower case). The number appears, plus a line-by-line breakdown marking which letters were added and which were subtracted.
3. Use the quick examples: the chips under each input (like 4, 9, 40, or MMXXVI) fill the field for you, which is handy for spot-checking the tricky subtractive cases.
4. Watch for validation: if you enter something out of range or a malformed numeral, the tool explains why and, where it can, suggests the correct spelling instead of guessing silently.

Worked example 1: writing 49 (and why it isn't IL)

A classic trap. To write 49, you might be tempted by "IL" - one before fifty. But subtraction only works between adjacent powers, and only with the six legal pairs. The correct path is 40 + 9 = XL + IX = XLIX. Break it down: XL is 50 minus 10 (40), and IX is 10 minus 1 (9). Together, XLIX = 49. The converter rejects IL and points you to XLIX.

Worked example 2: decoding MCMLXXXIV

Suppose you find MCMLXXXIV on a building. Read it in chunks, left to right: M = 1000, CM = 900, L = 50, XXX = 30, IV = 4. Add them up: 1000 + 900 + 50 + 30 + 4 = 1984. The two subtractive pairs (CM and IV) are the only places you subtract; everything else simply adds. Paste it into the "Roman → Number" tab and you will see exactly this sequence.

Worked example 3: the year 3999, the upper limit

The largest value this tool produces is 3999 = MMMCMXCIX. It splits as MMM (3000), CM (900), XC (90), and IX (9). You cannot go higher with standard letters because M can repeat only three times, capping the thousands at 3000. To represent 4000 or more, scribes drew a bar (vinculum) over a symbol to multiply it by 1000 - but that is outside the common standard, so the converter stops at 3999.

Who this converter is for

• Students learning the system for a math or history class, who want to check homework and see the breakdown.
• Writers and editors formatting copyright dates, volume numbers, outline headings, or appendix labels.
• Designers and tattoo artists rendering a meaningful year or date and wanting to confirm the spelling before it is permanent.
• Genealogists and history buffs decoding dates on gravestones, cornerstones, and old documents.
• Trivia and puzzle fans who just need a fast, accurate translation in either direction.

Key terms explained

• Additive notation: writing symbols in descending order and summing them (LXVI = 50 + 10 + 5 + 1 = 66).
• Subtractive notation: placing one smaller symbol before a larger one to subtract it, using only IV, IX, XL, XC, CD and CM.
• Vinculum: an overline placed above a numeral to multiply its value by 1000, used historically for numbers above 3999. Not supported here.
• Place value: the idea that a digit's position changes its value (the "2" in 20 vs 200). Roman numerals have no place value, which is why they are clumsy for arithmetic.
• Canonical form: the single correct spelling of a number. There is exactly one valid Roman numeral for each value from 1 to 3999, which is why IIII and IL are treated as errors.

A short history

Roman numerals grew out of marks used by the ancient Romans and dominated European counting for well over a thousand years. They were gradually displaced for calculation by the Hindu-Arabic system (the 0-9 digits we use today), which has both a zero and place value - making addition, multiplication, and long division far easier. Roman numerals never disappeared, though. They survive wherever a number is meant to feel formal, traditional, or decorative: on clock faces, in book front matter, in the names of monarchs and popes, and in the year stamped on films and buildings.

Popular Roman numeral conversions

Some numbers come up far more often than others - usually recent years, round milestones, and the values stamped on movies, copyrights, and anniversaries. Here are common conversions you can verify in the tool above:

Notice the pattern in the years: every "9" decade or century forces a subtractive pair. 1990 needs CM (900) and XC (90); 2024 needs the IV at the end. Those subtractive spots are where most handwritten Roman numerals go wrong, so they are worth double-checking.

Encoding vs decoding: which direction do you need?

People reach for this tool for two opposite jobs, and the converter handles both with its two tabs.

Encoding (Number → Roman) is for when you know the value and want the letters - the most common case being a year for a tattoo, a wedding date, a copyright line, or a chapter heading. You type 2026 and read back MMXXVI. The risk here is producing a non-standard form by hand (writing XXXX instead of XL), which the converter avoids by always returning the single canonical spelling.

Decoding (Roman → Number) is for when you found the letters and want the value - reading a cornerstone, a film's release year, a clock, or a monarch's title. You paste MCMLXXXIV and read back 1984. The risk here is misreading a subtractive pair as additive (treating CM as 1100 instead of 900), which the line-by-line breakdown prevents by labeling each step. When accuracy matters, do both: encode your number, then decode the result, and confirm you land back where you started.

Tips for reading and writing them

• Work by place: convert thousands, hundreds, tens, and ones separately, then join them (1984 = 1000 + 900 + 80 + 4 = M + CM + LXXX + IV).
• Only six subtractions exist: if a pair is not IV, IX, XL, XC, CD or CM, it is not a legal subtraction.
• Never repeat more than three: III is fine, IIII is not; the fourth step is always a subtractive pair.
• V, L and D never repeat: you will never see VV, LL or DD - the next larger symbol replaces them.
• When in doubt, verify both ways: convert your number to Roman, then convert that result back. If you land on the original number, the spelling is right.

Limitations and assumptions

This converter sticks to the common, modern standard taught in schools and used by major style guides. Keep these boundaries in mind:

• It covers 1 to 3999 only. There is no symbol for zero or negative numbers, and 4000 and above need the non-standard overline (vinculum), which is not supported.
• It uses strict canonical spelling. Numerals that some sources or clock faces tolerate - IIII for 4, or invented pairs like IL - are flagged as errors rather than silently accepted.
• It handles whole numbers only. The ancient fractional symbols (such as S for one half) are not part of normal Roman numerals and are out of scope.
• It ignores ornamental and medieval variants such as the "apostrophus" forms or additive year styles; the goal is one unambiguous result per value.

Related concepts and tools

Roman numerals are a number system without place value or a zero, which makes them a useful contrast to the decimal system you use every day. The most common reason people reach for them is dates and years, where this tool handles the formatting and a sister calculator handles the arithmetic:

• To count the days, months, or years between two dates before formatting one as a numeral, use the Date Calculator.
• To work out an exact age or anniversary from a birth or event year, use the Age Calculator.
• To find which week of the year a Roman-dated event falls in, see the Week Number Calculator.
• For another base-conversion exercise without place value quirks, the Binary Calculator and Scientific Notation Calculator show how other number systems represent the same value.

For other quick everyday conversions, browse the Everyday & Time category.