Roman Numeral Converter
Type a number or a Roman numeral and the other box fills in. Values from 1 to 3999 are checked for the standard form.
このコンテンツは英語です。
Symbols
計算例
Converting 1994 to Roman numerals
1994
MCMXCIV
A smaller letter before a larger one is subtracted, so CM is 900 and XC is 90.
Reading XLII as a number
XLII
42
XL is 40 and II is 2, which adds to 42.
Roman Numeral Converter について
A Roman numeral converter changes an ordinary number into its Roman form, such as 1994 becoming MCMXCIV, and turns a Roman numeral back into a number. Roman numerals still appear on clocks, monuments, book chapters, film credits and the names of kings and popes, so it helps to be able to read and write them. This tool works in both directions, and you can type into either box. The number box accepts values from 1 to 3999, which is the range of the standard form.
Roman numerals use seven symbols, I, V, X, L, C, D and M, and a smaller symbol placed before a larger one is subtracted from it. The tool checks that each Roman numeral follows the standard rules, so it rejects forms such as IIII for 4 or VX, and explains the problem in plain words. Below the boxes it also shows how the number is built up, such as 1994 being M, then CM, then XC, then IV, which makes the result easy to check.
Roman Numeral Converter の使い方
- Type a whole number from 1 to 3999 into the Number box to see its Roman numeral.
- Or type a Roman numeral into the Roman numeral box to see its number.
- Read the message under the boxes if a value is not accepted, and correct the letters or the number.
- Look at the line showing how the number is made up to check the result for yourself.
主な使いみち
- Writing a year or a chapter number in Roman numerals on a document
- Reading the year of a building or monument inscription
- Checking a Roman numeral in a film credit or book preface
- Teaching students how the subtraction rule works
よくあるご質問
How do I convert a number to a Roman numeral?
Type the whole number from 1 to 3999 into the Number box, and the Roman numeral appears in the other box straight away. For example 58 becomes LVIII, which is L for 50 followed by three I for 3. The line underneath shows each part of the number so you can see how the result was built.
What is the largest number that can be written in Roman numerals?
The standard form used here goes up to 3999, which is written MMMCMXCIX. Larger numbers need extra symbols, such as a line drawn over a letter to multiply it by a thousand, and those are not part of the usual system. This tool stops at 3999 so that every result follows the standard rules that most people learn.
Why does the Roman numeral 4 not look like IIII?
The standard form writes 4 as IV, which means one less than five. Writing IIII is an older style that appears on some clock faces and in some traditional inscriptions, but the standard rule is that the subtraction form is used. This tool treats IIII as invalid so the result matches the usual rules, and it tells you why.
Does Roman numerals have a zero?
No. The Roman system has no symbol for zero, so the smallest number that can be written is 1. If you type 0 in the number box, the tool explains that there is no Roman numeral for zero and asks for a number from 1 to 3999 instead.
Can I type Roman numerals in lower case?
Yes. The tool accepts lower case letters and changes them to capitals as it checks them, so mcmxciv gives 1994 just as MCMXCIV does. The letters themselves must still be in the standard order, and only I, V, X, L, C, D and M are valid.