Roman Numerals Converter

What is a Roman numerals converter?

A Roman numerals converter translates ordinary numbers (the Hindu-Arabic numerals 0–9 we use every day) into Roman numerals, and Roman numerals back into numbers. Type 2026 and you get MMXXVI; type MCMXCIV and you get 1994. This converter also turns a full date – a birthday, wedding date or anniversary – into Roman numerals for a tattoo, invitation or engraving, and it checks your input so you never copy an invalid numeral.

It covers every standard Roman numeral from 1 (I) to 3999 (MMMCMXCIX), shows the working step by step, and explains any mistake in plain words.

How to use the Roman numeral converter

1. Choose the direction: number → Roman, Roman → number, or date → Roman.
2. Enter a whole number from 1 to 3999, type the Roman letters (upper or lower case), or pick a date.
3. Read the result and the step-by-step table showing how it was built.

Roman numerals chart

Roman numerals use seven letters. Everything else is built from them:

Roman numerals 1 to 20

Tens, hundreds and thousands

With this Roman numerals chart you can write any number from 1 to 3999: write the thousands, then the hundreds, tens and ones, and join them. It works well as a printable chart for kids in class 3, class 5 or grade 4.

Roman numerals conversion rules

1. Add when the values go down or stay equal. VI = 5 + 1 = 6; XXI = 10 + 10 + 1 = 21; MDC = 1000 + 500 + 100 = 1600.
2. Subtract when a smaller letter comes before a larger one. IV = 5 − 1 = 4; XC = 100 − 10 = 90.
3. Only six subtraction pairs are allowed: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). So 99 is XCIX, not IC, and 49 is XLIX, not IL.
4. Repeat I, X, C and M at most three times in a row. 3 = III, but 4 = IV, not IIII.
5. Never repeat V, L or D. 10 is X, not VV.

The converter enforces all five rules, which is why it rejects inputs like IIII, VX, IC or MMMM.

How to calculate Roman numerals – worked examples

Number to Roman: 2026

Break it into place values: 2000 + 20 + 6. 2000 = MM, 20 = XX, 6 = VI. So 2026 = MMXXVI.

Number to Roman: 1994

1000 + 900 + 90 + 4 = M + CM + XC + IV = MCMXCIV.

Roman to number: MDCCLXXVI

M (1000) + D (500) + CC (200) + L (50) + XX (20) + V (5) + I (1) = 1776, the year of the US Declaration of Independence.

Roman to number: CXXXIX and XXVIII

CXXXIX = 100 + 30 + 9 = 139. XXVIII = 10 + 10 + 5 + 3 = 28. And MCCXIII = 1000 + 200 + 10 + 3 = 1213.

Roman numerals converter for dates, birthdays and tattoos

Choose Date → Roman numerals to convert a date of birth or an anniversary. Each part – day, month and year – is converted separately and joined with dots, dashes or spaces. For example, 15 August 1995 in the Indian and UK order (day, month, year) is XV · VIII · MCMXCV; in US order (month, day, year) it is VIII · XV · MCMXCV.

Before you get a Roman numerals tattoo, decide the date order, double-check it here, and ask the artist to copy the exact letters. A common mistake is writing 4 as IIII or 1999 as IMM; the correct form is MCMXCIX. Clock faces are the famous exception – many use IIII for 4 for visual balance.

Where Roman numerals are used today

• Clocks and watches (I to XII).
• Years on films, buildings and monuments – MMXXVI for 2026.
• Book chapters, prefaces (i, ii, iii) and outline lists.
• Names of kings, queens and popes, like Charles III, and events such as the Super Bowl.
• Chemistry: oxidation states in names such as iron(III) oxide, where the Roman numeral is the charge on the metal ion (Fe³⁺).

Roman numeral converter logic (JavaScript and Python)

Building a Roman numeral converter is a classic coding exercise – it appears in the freeCodeCamp JavaScript projects and as LeetCode problems 12 and 13. The logic behind this converter is short:

• Number to Roman: keep a list of the 13 values from largest to smallest (1000 M, 900 CM, 500 D, 400 CD, 100 C, 90 XC, 50 L, 40 XL, 10 X, 9 IX, 5 V, 4 IV, 1 I). Repeatedly subtract the largest value that fits and append its letters.
• Roman to number: read the letters left to right; if a letter is smaller than the next one, subtract it, otherwise add it.
• Validation: a single regular expression, ^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$, accepts every valid numeral from 1 to 3999 and rejects everything else.

The same three steps translate directly into a Roman numeral converter in Python, Java or C++.

Are there J, K, G or Z in Roman numerals?

No. Only I, V, X, L, C, D and M are Roman numerals. Letters such as J, K, G, R or Z have no numeric value, so a converter cannot turn a name or word into Roman numerals letter by letter. In some medieval manuscripts a final I was written as J (for example iij for 3), but that is a writing style, not a separate numeral.

What about zero, 4000 and 5000?

There is no Roman numeral for zero – the Romans had no symbol for it. Standard notation stops at 3999 because M may be repeated only three times. Larger numbers such as 5000 were written with a bar over the letter (vinculum), which multiplies it by 1,000: V̄ = 5,000 and X̄ = 10,000. Because bar notation is not standard in fonts and is easily misread, this converter sticks to 1–3999. For number systems computers use, try the binary calculator.

Homework, building dates and engravings

This Roman numerals converter calculator works both ways, so you can check homework, decode a year on a building or plan an engraving without memorising every rule, and it runs online with no app or sign-up.

How Roman numerals convert into numbers

To see how Roman numerals convert into numbers, split the numeral into chunks for thousands, hundreds, tens and ones. MCCXIII splits into M | CC | X | III = 1000 + 200 + 10 + 3 = 1213, which is why the Roman numeral converter shows MCCXIII = 1213. In the same way CXXXIX = 139, so a Roman numerals to digit converter simply adds the chunk values.

Roman numerals convert to Hindu-Arabic numbers

The digits 0–9 are called Hindu-Arabic numerals. When Roman numerals convert to Hindu-Arabic form, the answer is the ordinary number: XXVIII becomes 28 and MMXXVI becomes 2026. The converter does this instantly in the Roman → number mode.

Roman numerals converter from English words

If you have a number written in English, such as "two thousand and twenty", write it as digits first (2020) and then use the Roman numerals converter: 2020 is MMXX. A Roman numerals converter: English words go in only as numbers, and it cannot translate ordinary letters of a name, because only I, V, X, L, C, D and M carry values.

Roman numerals converter 2020 and other recent years

With the Roman numerals converter, 2020 is MMXX, 2021 is MMXXI, 2024 is MMXXIV, 2025 is MMXXV and 2026 is MMXXVI.

Roman numerals converter: date and time

For a date and time, convert each part on its own. 10:45 on 19 September 2026 can be written X:XLV · XIX · IX · MMXXVI. There is no Roman numeral for zero, so a time such as 10:05 is written X:V and midnight is usually written XII.

Roman numeral converter: month, day, year order

For a US-style date, a Roman numeral converter uses month, day, year: 9 July 1995 is VII.IX.MCMXCV. Most of the world writes day, month, year, giving IX.VII.MCMXCV. Pick one order and use it consistently, especially on a tattoo.

Roman numerals chart for kids (class 3, grade 4, class 5 and KS2)

A Roman numerals chart for kids works best when it starts small. In class 3 and grade 4, children usually learn I, V and X and the numbers 1 to 39; by class 5 and KS2 (UK Key Stage 2) they add L, C, D and M and read years. The Roman numerals chart KS2 pupils use goes up to 1000 (M). Print the tables above and cover a column to turn the chart into a quiz.

Roman numerals chart with matchsticks

A Roman numerals chart with matchsticks is a popular classroom activity because each numeral is made of straight strokes. I uses one stick, V and X use two, and L uses two. Ask children to build numbers and count the sticks: VIII needs five (two for V and three for the I strokes), and XIV needs five too.

Roman numerals chart in letters

In letters the Roman numerals chart is short: I = one, V = five, X = ten, L = fifty, C = one hundred, D = five hundred and M = one thousand.

Roman numerals chart: all numbers from 1 to 3999

You do not need a Roman numerals chart of all numbers. With the tables above you can build any number up to 3999, and this converter works as a Roman numerals chart generator: type any number to get its Roman form with the steps.

Roman numeral converter freeCodeCamp solution

The freeCodeCamp project asks you to write a function that turns a number into Roman numerals. A short JavaScript solution:

function convertToRoman(n) { const v = [1000,900,500,400,100,90,50,40,10,9,5,4,1]; const s = ['M','CM','D','CD','C','XC','L','XL','X','IX','V','IV','I']; let r = ''; v.forEach((x, i) => { while (n >= x) { r += s[i]; n -= x; } }); return r; }

Roman numerals converter in Python and Java

A Roman numerals converter in Python uses the same greedy loop: for value, sym in pairs: while n >= value: out += sym; n -= value. The Roman numerals converter Java version is identical, with two arrays and a StringBuilder.

How to calculate Roman numerals in chemistry

In chemistry, a Roman numeral in a compound name is the charge (oxidation state) on the metal. To calculate it, make the total charge zero: in FeCl₃ each chloride is −1, so iron is +3 and the name is iron(III) chloride. In CuO oxygen is −2, so copper is +2: copper(II) oxide.

Why XXMX is not valid in a Roman numerals converter online

People often type XXMX into a Roman numerals converter online, free tools included, hoping for 2010. It is not a valid numeral: X may be subtracted only from L and C, never from M. The correct form of 2010 is MMX, and 2020 is MMXX.

Frequently asked questions

Last updated 2026-09-18