Roman Numeral Converter

Convert Roman numerals and whole numbers

This converter works in both directions. Enter a positive whole number to write it as a Roman numeral, or enter a Roman numeral to return its Arabic-number value. Single-value mode validates the modern conventional form instead of accepting any sequence that happens to add to a number. Date and multiple-value mode converts each separated component while preserving the separator and order.

Roman numeral symbols and values

Roman numerals do not have a standard symbol for zero in the system used by this calculator. Negative values, decimals, and fractions also need a different notation, so the accepted numeric range begins at 1.

How numbers become Roman numerals

The converter repeatedly matches the largest available Roman value and subtracts it from the number. The subtractive pairs are included in the value list, so 900 becomes CM, 90 becomes XC, and 9 becomes IX. For example, 2026 is split into 2,000 + 20 + 6:

2026 = 1000 + 1000 + 10 + 10 + 5 + 1
2026 = M + M + X + X + V + I = MMXXVI

The result uses uppercase symbols and the common modern subtractive form. It writes 4 as IV rather than IIII, 40 as XL rather than XXXX, and 900 as CM rather than DCCCC.

How Roman numerals become numbers

Read the symbols from left to right. A symbol normally adds its value. When a smaller symbol appears immediately before a permitted larger symbol, the smaller value is subtracted as part of a pair. In MCMXCIV, M adds 1,000, CM adds 900, XC adds 90, and IV adds 4, producing 1,994.

MCMXCIV = M + CM + XC + IV
1,994 = 1,000 + 900 + 90 + 4

After calculating the value, this tool converts the answer back to Roman form and compares it with the input. That round-trip check catches nonstandard strings such as IIII, VX, IL, and repeated V symbols instead of silently assigning them a misleading result.

Standard subtractive pairs

I is subtracted only in IV and IX; X is subtracted in XL and XC; C is subtracted in CD and CM. V, L, and D are not used as subtractive symbols in this convention.

Roman numerals larger than 3,999

There is no single universally used modern notation for every large Roman numeral. This calculator uses a vinculum-style convention: an overline multiplies a symbol by 1,000. It accepts an underscore before each overlined input symbol because that is practical to type. For example, _V means V with an overline, or 5,000. Results show both the visual overline and the underscore input form.

_V = 5,000
_X = 10,000
_M = 1,000,000

The supported range ends at 3,999,999. Within that range, the thousands portion is converted to ordinary Roman form and each of those symbols receives an overline. This makes the rule predictable while keeping the ordinary 1 through 3,999 notation unchanged.

Roman numeral date converter

Select date or multiple-value mode to convert components separated by a slash, hyphen, period, backslash, vertical bar, or space. For example, 9/27/2026 becomes IX/XXVII/MMXXVI. Entering IX/XXVII/MMXXVI converts it back to 9/27/2026. The converter preserves the sequence you enter; it does not guess whether a date is month/day/year, day/month/year, or year/month/day.

Each component is checked independently. This means the same mode can convert a list such as 12 49 2026 or XII XLIX MMXXVI. It does not validate calendar rules such as the number of days in a month; use the date calculator when calendar arithmetic or date validity is the goal.

Roman numeral writing rules

• Write values from largest to smallest except for the six standard subtractive pairs.
• I, X, C, and M may repeat up to three times in succession in ordinary modern notation.
• V, L, and D are not repeated.
• Use IV and IX for 4 and 9, XL and XC for 40 and 90, and CD and CM for 400 and 900.
• Letter case does not change the value; the converter normalizes valid input to uppercase.
• There is no zero symbol in the notation supported here.

Common examples

Frequently asked questions

What is 2026 in Roman numerals?

2026 is MMXXVI: MM is 2,000, XX is 20, and VI is 6.

Can Roman numerals represent zero?

Not in the conventional system used here. Enter a whole number from 1 upward.

Why is IIII sometimes seen on clocks?

Clock faces and historical inscriptions can use stylistic or nonstandard forms. This converter validates the common modern arithmetic convention and therefore returns IV for 4.

Are lowercase Roman numerals accepted?

Yes. Valid lowercase input is normalized to uppercase in the result.

Can I convert a date?

Yes. Choose date or multiple-value mode and enter separated numeric or Roman components. The original order and separators are preserved.