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Roman Numeral Converter

Convert ordinary integers and canonical Roman numerals in either direction, with a breakdown of the symbols.

Browser-based · No signup · Transparent assumptions

Open converter Free to use · No signup
  1. 01Enter your values
  2. 02Adjust your settings
  3. 03Review your results
All 23 utilities
Direction
Input
Enter any whole number from 1 to 3999.
Symbol reference
I
1
V
5
X
10
L
50
C
100
D
500
M
1000
⊂⊃
subtract
IV 4
IX 9
XL 40
XC 90
CD 400
CM 900
Export
Ⅻ

Enter a value to begin

Your conversion, step-by-step working, and validation will appear here.

Standard Latin symbols only. Range: 1–3999. Noncanonical forms are rejected rather than silently corrected.

Calculations run in this browser. Shared URLs can contain input values. Review links before sharing financial, dietary or birth-date information.

When to use this calculator

Check a year, chapter number or numeral exercise within the standard 1-3999 range. Use the place-value breakdown to understand subtractive forms such as IV and IX rather than accepting a nonstandard sequence of symbols.

Review the worked example and assumptions below, then use the supported report or copy controls to keep the result with its inputs. Calculations run in this browser; a shared URL can include the values you entered.

How to use Roman Numeral Converter

  1. Choose number-to-Roman or Roman-to-number mode.
  2. Enter an integer from 1 to 3999 or standard symbols I, V, X, L, C, D and M.
  3. Review the breakdown, copy the result or export a text report.

Standard subtractive notation

Roman numerals add symbol values, with six standard subtractive pairs: IV, IX, XL, XC, CD and CM. Canonical validation converts the parsed value back to Roman notation and compares it with the input, preventing forms such as IIX and VX.

Worked example

1987 = 1000 + 900 + 80 + 7
1987 = M + CM + LXXX + VII = MCMLXXXVII
XLII = 42

Assumptions and limits

Conventional modern notation only, 1–3999. There is no standard zero or negative numeral in this model. Overbars, historical additive forms such as IIII and Unicode numeral glyphs are not accepted. Lowercase Latin symbols are normalized.

Reference: Unicode: number forms and notation. Model/source review: 19 October 2026. See the tool-specific scope and precision limits above.

Frequently asked questions

Why is IIII rejected?

This converter enforces canonical subtractive notation, where four is IV. Clock faces may use historical variants.

Can it convert zero?

No. This notation has no zero symbol.

Can I enter lowercase?

Yes. Standard lowercase Latin letters are normalized before validation.

Use the converter’s canonical notation

Enter an allowed integer or supported Roman symbols and inspect the normalized output. Preserve any source notation separately if it uses a historical variant.

Scope of this workflow

This model excludes zero, negatives, overbars and historical additive spellings. It is a bounded conventional converter, not a parser for every inscription.

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