Roman Numerals to Numbers Converter Online Tool

Number

About Roman Numerals to Numbers Converter Online Tool:

This online Roman Numerals to Numbers Converter helps you to convert one Roman Numeral into a number (base 10). Put Roman Numeral into the first textbox, the number result will show in the second textbox.

Roman Numerals:

Roman numerals is invented by ancient Rome, it use letters from Latin ("I" for "1", "V" for "5", "X" for "10", "L" for "50", "C" for "100", "D" for "500", "M" for "1000") to represent numbers. Roman numerals is still widely used in academic paper chapter numbering system.

How to convert from Roman Numeral to Number?

Step 1: Remember the Latin letters list ('I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000). Remember its order and each value.
Step 2: From left to right, subtract a letter's corresponding value if it appears before a larger letter.

Example 2.1: IV = V − I = 5 − 1 = 4

Example 2.2: XL = X − L = 50 − 10 = 40
Step 3: In other case, add a letter's corresponding value.

Example 3.1: XXXV = X + X + X + V = 10 + 10 + 10 + 5 = 35

Example 3.2: CXXIII = C + X + X + I + I + I = 100 + 10 + 10 + 1 + 1 + 1 = 123

Example 1: Convert Roman Numeral "CXLVI" to Number:

CXLVI = C + XL + V + I = 100 + (500-10) + 5 + 1 = 146

Example 2: Convert Roman Numeral "CDXCIV" to Number:

CDXCIV = CD + XC + IV = (500-100) + (100-10) + (5-1) = 494

Roman Numerals to Numbers conversion table:

Roman Numerals	Numbers	Roman Numerals	Numbers
I	1	XXI	21
II	2	XXII	22
III	3	XXIII	23
IV	4	XXIV	24
V	5	XXV	25
VI	6	XXVI	26
VII	7	XXVII	27
VIII	8	XXVIII	28
IX	9	XXIX	29
X	10	XXX	30
XI	11	XXXI	31
XII	12	XXXII	32
XIII	13	XXXIII	33
XIV	14	XXXIV	34
XV	15	XXXV	35
XVI	16	XXXVI	36
XVII	17	XXXVII	37
XVIII	18	XXXVIII	38
XIX	19	XXXIX	39
XX	20	XL	40

More information:

Wikipedia (Roman numerals): https://en.wikipedia.org/wiki/Roman_numerals

Convert Roman Numerals to Numbers with Python:

def transform_roman_numeral_to_number(roman_numeral):
    roman_char_dict = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
    res = 0
    for i in range(0, len(roman_numeral)):
        if i == 0 or roman_char_dict[roman_numeral[i]] <= roman_char_dict[roman_numeral[i - 1]]:
            res += roman_char_dict[roman_numeral[i]]
        else:
            res += roman_char_dict[roman_numeral[i]] - 2 * roman_char_dict[roman_numeral[i - 1]]
    return res


roman_numeral_input = 'MMXVIII'
number_output = transform_roman_numeral_to_number(roman_numeral_input)
print('Roman numeral {0} equal to:{1}'.format(roman_numeral_input, number_output))

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Roman numeral MMXVIII equal to:2018

Convert Roman Numerals to Numbers with Java:

import java.util.Map;
import java.util.HashMap;

public class NumberConvertManager {
    public static int transform_roman_numeral_to_number(String roman_numeral) {
        Map<Character, Integer> roman_char_dict = new HashMap<Character, Integer>();
        roman_char_dict.put('I', 1);
        roman_char_dict.put('V', 5);
        roman_char_dict.put('X', 10);
        roman_char_dict.put('L', 50);
        roman_char_dict.put('C', 100);
        roman_char_dict.put('D', 500);
        roman_char_dict.put('M', 1000);
        int res = 0;
        for (int i = 0; i < roman_numeral.length(); i += 1) {
            if (i == 0 || roman_char_dict.get(roman_numeral.charAt(i)) <= roman_char_dict.get(roman_numeral.charAt(i - 1)))
                res += roman_char_dict.get(roman_numeral.charAt(i));
            else
                res += roman_char_dict.get(roman_numeral.charAt(i)) - 2 * roman_char_dict.get(roman_numeral.charAt(i - 1));
        }
        return res;
    }

    public static void main(String[] args) {
        String roman_numeral_input = "MMXVIII";
        int number_output = transform_roman_numeral_to_number(roman_numeral_input);
        System.out.println("Roman numeral " + roman_numeral_input + " equal to:" + number_output);
    }
}

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Roman numeral MMXVIII equal to:2018