Skip to content

Tools

EN

Roman Numerals to Numbers

Type a Roman numeral to get its value, broken down symbol by symbol so you can see where the number comes from.

How to read a Roman numeral

Read from left to right and add as you go: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. MMXXVI is 1000 plus 1000 plus 10 plus 10 plus 5 plus 1, which is 2026. As long as each letter is worth the same or less than the one before it, the numeral is simply a sum.

The one twist is subtraction. When a smaller letter sits directly before a larger one, it is taken away instead of added: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400 and CM is 900. Those six pairs are the entire list, so a numeral never holds a surprise beyond them. MCMXCIV is where this matters most: it reads as M, then CM, then XC, then IV, giving 1000 plus 900 plus 90 plus 4, which is 1994. Read letter by letter without spotting the pairs and you would get 1996.

Not every string of valid letters is a valid numeral, and this is where most converters quietly go wrong. IIII has an obvious reading of 4, VV looks like 10, and IC looks like 99, but none of the three is Roman notation. A converter that answers anyway hands you a plausible number with no warning that the input was never a numeral in the first place. This one checks by converting its own answer back: if the result does not reproduce exactly what you typed, the input was not canonical and it says so.

The range is 1 to 3999. There is no zero, because the system counts things and has no symbol for none, and there is no standard way to write 4000 or beyond, which would need a fourth M. Larger values used a bar over a letter to multiply it by a thousand, a separate notation that is not handled here.

One thing you will meet in the wild and that this tool will reject: the IIII on a clock dial. It is genuinely written that way, and it is genuinely not standard notation. Watchmakers adopted it before the rules settled and kept it because IIII at four balances VIII at eight on the face. If you are reading a clock rather than a number, that one is the exception.

Frequently asked questions

What number is MCMXCIV?

1994. It breaks into M for 1000, CM for 900, XC for 90 and IV for 4. The three subtractive pairs are what make it tricky: adding the letters one at a time without spotting them gives 1996.

Why does this reject IIII when I can see it on a clock?

Because IIII is not standard notation, even though clock faces really do use it. Watchmakers settled on it before the rules were fixed and kept it so that IIII at four balances VIII at eight on the dial. As a number, 4 is IV.

How do I know when to subtract?

Only when a smaller letter comes directly before a larger one, and only in six combinations: IV, IX, XL, XC, CD and CM. Everywhere else you add. Reading MCMXCIV as one letter at a time gives 1996; reading the pairs gives 1994.

Why is VV not 10?

Because V, L and D never repeat. Two of any of them would simply be the next symbol up, so VV would be X and there is no reason to write it the long way. The same goes for LL and DD.

What is the highest numeral I can enter?

MMMCMXCIX, which is 3999. Four M in a row is not standard notation, so MMMM is rejected rather than read as 4000.

Is my data sent anywhere?

No. The conversion runs in your browser in a few lines of JavaScript. There is no server to send it to: this site is static files.

Other tools