Roman Numerals to Number Converter

Going the other way? Convert a number back to Roman numerals →

How do you convert Roman numerals to numbers?

A Roman numeral is read left to right: MCMLXXXVII is 1987. Add the symbol values as you go, and where a smaller symbol stands before a larger one, subtract it instead. Grouping the symbols by decimal place first makes the arithmetic short enough to check by eye.

1. Type the numeral into the box. Either case works, and spaces are ignored.
2. Split it into place groups: the thousands first, then the hundreds, the tens and the units.
3. Read each group. A group where the larger symbol comes first is a sum; a group where the smaller comes first is a subtraction.
4. Add the groups together. The working under the box shows one line per group.
5. Copy the figure, or swap the direction to write a figure back out.

Roman Symbol Values and Common Years

Roman numerals use seven letters: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. The second table carries the years a reader meets most, each written by the same converter that answers the box above.

Worked Example: MCMLXXXVII to Number

MCMLXXXVII has four place groups. Three of them are sums and one is a subtraction, and the working below keeps them apart so the total can be checked a line at a time.

Adding the four groups gives 1987. The seed below is the one the page that writes numerals uses, so the two directions corroborate each other rather than standing alone.

Check it in reverse

To verify the result by hand, write the same figure back in Roman numerals and compare it with what you started from.

Worked examples: Roman numerals to numbers

Each example gives the value first, then the working. Select a value to load it in the converter.

Every example above reverses exactly — build the same value back out of the Roman symbols.

How Roman Numerals Are Read

The rules below decide what this converter accepts. Two of them are more generous than the usual summary: either case is read, and the older additive forms are read as well, because they are not mistakes.

What Makes a Roman Numeral Valid?

When a Symbol Is Taken Away

Only I, X and C are ever subtracted, and only from the next two larger symbols. That gives six subtractive forms and no others: IV, IX, XL, XC, CD, CM. That is why IL is refused and XLIX is accepted: the L can only lose an X, never an I.

The Older Form on a Clock Face

IV is the standard form of 4, but IIII is the older additive form and clock faces have used it since the late 14th century. This page reads IIII as 4 and tells you that IV is the standard form, rather than refusing a numeral that has been in use for six hundred years.

What Cannot Be Read

I, X, C and M may stand up to three times in a row; V, L and D are never repeated. A run of five, a repeated V, L or D, and a group whose places climb again are all refused, each with the rule it broke.

Common Mistakes

• Adding every symbol in order. In MCM the C is subtracted from the M, so the pair is 900 and the numeral is 1900, not 2100.
• Treating IIX as 8. Only one symbol is ever subtracted at a time, so 8 is VIII.
• Assuming a place can come back. Once the numeral has moved down to the tens it cannot return to the hundreds, so XCC is refused.
• Reading a lowercase numeral as something different. Case carries no meaning here, so mcm and MCM give the same figure.

Frequently Asked Questions

Related Conversions

• Words are the other notation this family reads — turn an amount written in words into digits.
• If you want words rather than a figure, spell a number out in words instead.

The rest of the family sits on the rest of the numeral converters.