Roman Numeral Converter to
Convert Between Roman and Arabic

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The Roman Numeral Converter on this page will convert Roman numerals to numbers and visa versa, and show its work.

This free online numeral calculator will convert Roman numerals into Arabic numbers and visa versa, plus display a conversion chart showing exactly how it arrived at the translation.

Plus, unlike other online conversion calculators, if you enter an invalid Roman numeral, the calculator on this page will even alert you to which rule or rules were broken by your entry.

Finally, the Roman numeral converter also provides a feature that will allow you to create your own custom, printable Roman numerals chart: 1-20, 1-100, 101-200, or whichever span of numbers you choose. Cool!

How to Read Roman Numerals

The first step in learning how to read Roman numerals is to familiarize yourself with the Arabic value represented by each letter -- which can be seen in the following chart:

Arabic Value of Roman Numerals

1 5 10 50 100 500 1000
I VXLCDM

The next step in learning how to read Roman numerals is to become aware of how the placement of numerals impacts the translated value. In that regard, there are two rules you need to be aware of when attempting to translate the numerals into values:

  1. If a letter representing an equal or greater value is placed directly in front of a letter representing an equal or smaller value, the two values are simply added together. For example, "XX" would translate to "20" and "XI" would translate to "11".
  2. If a letter representing a smaller value is placed directly in front of a letter representing a larger value, the smaller value is subtracted from the larger value. For example, "IX" would translate to "9" and "IV" would translate to "4".

The following conversion chart shows how you would read the Roman numeral "MMMCDLXII" -- which includes instances of both addition and subtraction:

How to Read the Roman Numeral "MMMCDLXII"

Place
Value
Roman
Numerals
Addition/Subtraction Arabic
Numerals
1000s MMM 1000 + 1000 + 1000 3000
100s CD 500 - 100 400
10s LX 50 + 10 60
1s II 1 + 1 2
Totals MMMCDLXII = 3462


Notice that in the 100s line, "CD" indicates a subtraction because "C" (100) is less than the "D" (500) it precedes. The above is how the Roman Numeral Converter shows its work.

How to Write Roman Numerals

In addition to the rules you have learned for reading Roman numerals, there are a few more rules you need to know when writing Roman numerals.

  1. A letter cannot be repeated more than 3 times in succession, and only powers of 10 can be repeated. In other words, "CCCC" is invalid, and "VVV" is invalid (5 is not a power of 10). The correct way to write 400, would be "CD" (500 - 100 = 400), and the correct way to write 15 would be "XV" (10 + 5 = 15).
  2. Only powers of 10 (1, 10, 100) can be subtracted from a larger value. Therefore you could not write 5 as "VX" (10 - 5 = 5) because 5 is not a power of 10.
  3. Only a single smaller value may precede a larger value. This means you could not write 3 as "IIV" (5 - 1 - 1 = 3) because "II" is placing 2 smaller values in front of a larger value.
  4. In the case of a smaller value being subtracted from a larger value, the larger value cannot be more than 10 times the smaller value. In other words, you cannot write 999 as "IM" (1000 - 1 = 999) because "M" is more than 10 times greater than "I". Instead you would write 999 as "CMXCIX" [(1000 - 100) + (100 - 10) + (10 - 1)]. Aren't you glad we use Arabic numbers?
  5. In order to write numerals greater than 3999 (without breaking any rules), you would need to place a line above the appropriate letters to indicate the value is a thousand times greater. For example, a "V" with a line above it would indicate 5000 (5 * 1000). Note that the Roman numeral converter does not accommodate numbers or numerals greater than 3999 (MMMCMXCIX).

With the above rules in mind, here is how you would write the Roman numeral for the Arabic number 2345:

Writing the Roman numeral for "2345"

Digit Place
Value
Addition/Subtraction Roman
Numerals
2 2000 1000 + 1000 MM
3 300 100 + 100 + 100 CCC
4 40 50 - 10XL
5 5 5 V
Totals 2345 = MMCCCXLV


The above is how the Roman Numeral Converter shows its work.

With that, let's use the Roman Numeral Converter to translate to and from Arabic numbers, or to create a custom, printable Roman numeral chart.

Roman Numeral Converter
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Instructions: Enter the an Arabic (whole) number or a Roman Numeral you would like to translate, and then click the "Convert Roman Numerals or Arabic Number" button.

Mouse over the blue question marks for a further explanation of each entry field. More in-depth explanations can be found in the glossary of terms located beneath the Roman Numeral Converter.

Help Arabic number or Roman numeral:
Help Translation:
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Roman Numeral Converter Glossary of Terms

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Roman numerals: Value expression system that uses letter symbols for counting and representing numeric values (I, II, III, IV, V, etc.) instead of numeric characters.

Arabic numbers: The counting and value expression system we are accustomed to, which uses numeric characters (1, 2, 3, 4, 5, etc.).

Arabic number or Roman numeral entry field: Enter either an Arabic number or a Roman numeral (leave no spaces before, within, or after numbers or numerals). Please note that the Roman numeral converter currently only accepts Arabic numbers up to 3999, and Roman numerals up to MMMCMXCIX.

Translation result field: This is the Arabic number or Roman numeral translation -- depending on which type you entered in the top of the Roman Numeral Converter.

Printable Roman Numeral Chart button: If you would like to print out a Roman numerals chart, enter the starting Arabic number in the From field and the ending Arabic number in the To field and click this button. Upon doing so, a new, printer friendly window will open displaying your custom Roman Numeral Chart. Note that the chart will be five columns wide, so try to enter spans that are divisible evenly by 5 (1-20, 1-100, 101-200, etc.).

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