Roman Numeral Converter to Convert Between Roman and Arabic

Roman Numeral Converter Sign

This calculator will convert Roman numerals into Arabic numbers or the reverse, 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!

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Roman Numeral Converter

Convert Roman numerals to numbers or the reverse. Or create a conversion chart.

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Selected Data Record:

A Data Record is a set of calculator entries that are stored in your web browser's Local Storage. If a Data Record is currently selected in the "Data" tab, this line will list the name you gave to that data record. If no data record is selected, or you have no entries stored for this calculator, the line will display "None".

DataData recordData recordSelected data record: None
Arabic number keypad
Arabic Number Keypad
The following will be entered into the underlying field automatically as you tap the keys.
Roman numeral keypad
Roman Numeral Keyboard
The following will be entered into the underlying field automatically as you tap the keys.
 

Arabic number or Roman numeral:

Enter either an Arabic number or a Roman numeral (leave no spaces before, within, or after numbers or numerals). For easier entry, tap the plus (+) icon to open the appropriate keypad.

Please note that the Roman numeral converter currently only accepts Arabic numbers up to 3999, and Roman numerals up to MMMCMXCIX.

Translation:Translation:Translation:Translation:

Translation:

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

If you would like to save the current entries to the secure online database, tap or click on the Data tab, select "New Data Record", give the data record a name, then tap or click the Save button. To save changes to previously saved entries, simply tap the Save button. Please select and "Clear" any data records you no longer need.

Create Conversion Chart

Roman numeral conversion chart:

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

From number:From number:From whole number:From whole number:

Starting number:

Enter the whole number you want the chart to start with.

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To number:To number:To whole number:To whole number:

Ending number:

Enter the whole number you want the chart to stop at.

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Help and Tools

Learn

How to read and write Roman numerals.

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

1510501005001000
IVXLCDM

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 or SubtractionArabic
Numerals
1000sMMM1000 + 1000 + 10003000
100sCD500 - 100400
10sLX50 + 1060
1sII1 + 12
TotalsMMMCDLXII=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. 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"

DigitPlace
Value
Addition or SubtractionRoman
Numerals
220001000 + 1000MM
3300100 + 100 + 100CCC
44050 - 10XL
555V
Totals2345=MMCCCXLV

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

Adjust Calculator Width:

Move the slider to left and right to adjust the calculator width. Note that the Help and Tools panel will be hidden when the calculator is too wide to fit both on the screen. Moving the slider to the left will bring the instructions and tools panel back into view.

Also note that some calculators will reformat to accommodate the screen size as you make the calculator wider or narrower. If the calculator is narrow, columns of entry rows will be converted to a vertical entry form, whereas a wider calculator will display columns of entry rows, and the entry fields will be smaller in size ... since they will not need to be "thumb friendly".

Show/Hide Popup Keypads:

Select Show or Hide to show or hide the popup keypad icons located next to numeric entry fields. These are generally only needed for mobile devices that don't have decimal points in their numeric keypads. So if you are on a desktop, you may find the calculator to be more user-friendly and less cluttered without them.

Stick/Unstick Tools:

Select Stick or Unstick to stick or unstick the help and tools panel. Selecting "Stick" will keep the panel in view while scrolling the calculator vertically. If you find that annoying, select "Unstick" to keep the panel in a stationary position.

If the tools panel becomes "Unstuck" on its own, try clicking "Unstick" and then "Stick" to re-stick the panel.