Roman Numerals: Chart, Rules and Converter

Roman numerals are the number system of ancient Rome, written with seven letters: I, V, X, L, C, D and M. You still see the Roman number system on clock faces, in book chapters, in exam question numbers, on building plaques and in movie sequels. This guide explains every rule in simple steps, and the converter lets you change any number from 1 to 3999 into Roman numerals and back.

What is a Roman number?

A Roman number is a number written with letters instead of digits. There is no symbol for zero, and there is no place value. Instead, you add and subtract the values of the letters. That is why a small number like 8 needs four letters (VIII) while 50 needs only one (L).

Roman numerals chart: the 7 symbols

Learn these seven first. A handy line to remember the order is "I Value Xylophones Like Cows Do Milk", which gives I, V, X, L, C, D, M.

Rule 1: add when a letter is equal or smaller

Read from left to right. If a letter is the same as or smaller than the one before it, add it. So VI is 5 + 1 = 6, XIII is 10 + 1 + 1 + 1 = 13, and CLX is 100 + 50 + 10 = 160.

Rule 2: subtract when a smaller letter comes first

If a smaller letter sits just before a bigger one, take it away. Only six pairs are allowed:

So 4 is IV, not IIII, and 90 is XC, not LXXXX. You cannot write 99 as IC or 49 as IL. Break the number into tens and ones first: 99 is 90 + 9, which gives XCIX, and 49 is 40 + 9, which gives XLIX.

Rule 3: repeat a letter at most three times

I, X, C and M can repeat up to three times in a row, as in III, XXX and CCC. V, L and D never repeat, because VV would just be X. This is also why the standard system stops at MMMCMXCIX (3999).

How to write any number in Roman numerals

1. Split the number into thousands, hundreds, tens and ones.
2. Write each part using the chart and the six subtraction pairs.
3. Join the parts from left to right, biggest first.

Here are some worked examples:

For instance, 1500 ka Roman number is MD: M for 1000 and D for 500.

How to read Roman numerals

To turn a Roman numeral back into a number, scan it from left to right. Look for the six subtraction pairs first, then add everything up. Take MMMXXXVI: MMM is 3000, XXX is 30 and VI is 6, so the total is 3036. A few more:

Invalid Roman numerals

Some letter strings look like Roman numerals but break the rules. You may see forms like XXVXX, IXXXI or XXMX in puzzles, tattoos or social posts. None of these is a valid Roman numeral, because a V cannot sit between X letters that way, I cannot come before XXX, and X cannot be subtracted from M. If you type them into the converter above, it will tell you they are not valid. Ask the person what number they meant, then write it the standard way.

Where Roman numerals are used today

• Clock and watch faces (many use IIII instead of IV, a style choice, not the standard rule).
• Chapter, part and volume numbers in books.
• Question numbers and sub parts in exam papers, often in small letters like i, ii, iii, iv.
• Names of kings, queens and popes, such as a ruler called the Second, written II.
• Outline lists, film sequels and stone plaques on buildings.

Small letters work the same way: iv is 4 and xii is 12. For full lists, see Roman numerals 1 to 100 and Roman numerals 1 to 1000, or open a single page such as 4 in Roman numerals, 40 in Roman numerals or 999 in Roman numerals.