Roman Numeral Converter

1. Choose a direction: number to Roman, or Roman to number.
2. Enter a number from 1 to 3999, or a Roman numeral.
3. Read the result.
4. See your input and the conversion written out.

Here is what each result means:

Roman numerals are a number system from ancient Rome that uses letters to stand for values. Seven letters do all the work: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. Numbers are built by writing these from largest to smallest and adding them up, so LXVII is 50 plus 10 plus 5 plus 1 plus 1, which is 67.

To avoid four of the same letter in a row, the system uses a subtractive rule. A smaller letter placed before a larger one is subtracted, which gives the neat forms IV for 4, IX for 9, XL for 40, XC for 90, CD for 400 and CM for 900. So 2024 is MMXXIV: two thousands, then twenty, then four written as IV.

Roman numerals are still seen today on clock faces, in book chapters, on film credits and for the numbers of monarchs and events, such as Super Bowl LVIII. They have no symbol for zero and no simple way to write very large numbers, so in everyday use they are limited to the range 1 to 3999.

It converts in whichever direction you choose.

1. For a number, take the largest value that fits, write its letters, subtract it, and repeat.
2. For a Roman numeral, add the letter values, subtracting any smaller letter that sits before a larger one.
3. The converter checks the result is a valid, standard numeral.

For other number tools, see the number to words converter and the base converter.

Convert 2024 to a Roman numeral.

Result: 2024 is MMXXIV: MM is 2000, XX is 20, and IV is 4. Going the other way, IX reads as 9, since the I before the X is subtracted from it.

Every Roman numeral is built from these seven letters.

The values are 1 and 5 scaled up by powers of ten. Between them, the subtractive pairs handle the fours and nines, so no letter needs to be repeated more than three times in a row.

The subtractive rule keeps numerals short.

The additive forms, like IIII for 4, are sometimes still seen on clock faces, but the subtractive forms are the modern standard. This converter reads both but always writes the standard subtractive version.

The Order of Letters

Letters go largest to smallest, except for the subtractive pairs, where a smaller letter comes first.

The Subtractive Rule

Only I, X and C are subtracted, and only before the next one or two larger letters.

The Range

Standard numerals cover 1 to 3999; there is no zero and no simple form above that.

Reading Numerals

Decode a year, chapter or clock face written in Roman numerals.

Writing Numerals

Turn a year or number into its Roman form for a title or design.

Learning

Check your own conversions while learning the system.

1. Repeating a Letter Four Times

Use IV, not IIII, and XL, not XXXX. A letter appears at most three times in a row.

2. Subtracting the Wrong Letters

Only I, X and C are subtracted, and only from the next larger values, such as IX or XC.

3. Expecting a Zero

Roman numerals have no symbol for zero, so counting starts at I for 1.

4. Going Above 3999

Numbers above 3999 need a bar or brackets, which are outside the standard system.

5. Wrong Order

Writing letters out of order, such as IM for 999, is not valid; 999 is CMXCIX.

Conversions are exact within the standard 1 to 3999 range.

2024 is MMXXIV. MM is 2000, XX is 20 and IV is 4, giving MMXXIV.

I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. All Roman numerals are built from these.

A smaller letter before a larger one is subtracted. So IV is 4 (5 minus 1) and IX is 9 (10 minus 1), instead of writing IIII or VIIII.

In the standard system it is MMMCMXCIX, which is 3999. Larger numbers need a bar over a letter to multiply it by 1000, which is not standard.

No. The Roman system has no symbol for zero. Counting begins at I for 1.

Add the letter values from left to right, but subtract any smaller letter that sits directly before a larger one. LIX is 50 plus (10 minus 1), which is 59.

That is the older additive form of 4. Many clock faces keep it for tradition and balance, though IV is the modern standard.

No. They represent whole positive numbers only, with no decimals, fractions or negative values in the standard system.

No. The calculation runs in your browser and nothing you enter is stored or sent anywhere, unless you choose Save, which keeps the result only on this device.

• Roman numerals (Wikipedia).
• Subtractive notation (Wikipedia).
• Roman numerals explained (Maths Is Fun).