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Roman Numeral Converter

Use this Roman Numeral Converter to switch between Arabic numbers (1–3999) and Roman numerals. Choose a mode, then fill in the matching input.

Enter this when converting Number to Roman numeral. Valid range is 1–3999.

Enter this when converting Roman numeral to number. Use standard letters I, V, X, L, C, D, M (uppercase recommended).

Convert between Roman numerals and Arabic numbers in seconds. Our Roman Numeral Converter validates inputs, applies standard rules, and delivers clear, readable results for values from 1 to 3999.

What the Roman Numeral Converter does

The Roman Numeral Converter translates whole numbers (1–3999) into their Roman numeral equivalents and converts valid Roman numerals back to Arabic numbers. It follows the conventional rules of Roman notation, including subtractive pairs like IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). Whether you are studying history, checking dates for a project, or formatting an outline, this tool ensures accurate, standards-based conversions.

How to use the converter

  1. Choose your conversion mode: Number to Roman numeral, or Roman numeral to number.
  2. If converting a number, enter an integer between 1 and 3999.
  3. If converting a Roman numeral, type a valid sequence using I, V, X, L, C, D, M.
  4. Click Convert to see the result instantly.

Tip: Roman numerals are typically written in uppercase. While the converter accepts lowercase input, results are normalized using standard uppercase symbols.

Roman numeral basics and rules

Roman numerals use letters to represent values. The core symbols are:

  • I = 1
  • V = 5
  • X = 10
  • L = 50
  • C = 100
  • D = 500
  • M = 1000

Numbers are formed by adding values from left to right, with limited subtraction to avoid four identical symbols in a row. For example, III = 3, but 4 is IV (not IIII). Likewise, 9 is IX, 40 is XL, 90 is XC, 400 is CD, and 900 is CM. The conventional maximum represented without special notation is 3999 (MMMCMXCIX).

Valid patterns

Standard notation limits repeats and the order of symbols. Common guidelines include:

  • I, X, C, and M may be repeated up to three times in succession.
  • V, L, and D should not be repeated.
  • Subtractive notation only uses I before V or X; X before L or C; C before D or M.

These rules help avoid ambiguity and keep the numerals concise and readable.

Examples

  • 2024 = MMXXIV
  • 1492 = MCDXCII
  • 3999 = MMMCMXCIX
  • MCMLXXXVII = 1987

Why use this Roman Numeral Converter?

Accuracy matters when dealing with traditional numeral systems. This converter checks your input against standard patterns and outputs the correct representation without guesswork. It’s ideal for students, teachers, designers, writers, and anyone who needs quick, error-free conversions in a familiar web form.

Best practices

  • Stick to uppercase for clarity: e.g., "XLII" instead of "xlii".
  • Keep within the 1–3999 range for standard formatting.
  • Use subtractive pairs where applicable to avoid long sequences of repeated characters.

Because the tool adheres closely to the established rules, it prevents invalid combinations and helps you learn by example. As you convert, you’ll quickly internalize patterns like XC for 90 and CD for 400, making manual reading and writing of Roman numerals more intuitive over time.

FAQs

How does the Roman Numeral Converter handle invalid inputs?

It validates format and range (1–3999). If the input breaks standard rules, it returns an error with guidance.

Can the Roman Numeral Converter convert lowercase letters?

Yes. It accepts lowercase input and normalizes it to uppercase before validation and conversion.

What range does the Roman Numeral Converter support?

Standard Roman numerals from 1 to 3999, covering values up to MMMCMXCIX.

Does the Roman Numeral Converter use subtractive notation?

Yes. It uses standard pairs like IV, IX, XL, XC, CD, and CM for concise, correct results.

Why did the Roman Numeral Converter reject my numeral?

It likely violates rules on ordering or repeats (e.g., IIII or VX). Adjust to standard notation and retry.

Is the Roman Numeral Converter suitable for educational use?

Absolutely. It enforces canonical rules, making it helpful for learning and checking homework.

Can the Roman Numeral Converter show 0 or negative numbers?

No. Roman numerals have no zero or negatives; the supported range is 1–3999.

Will the Roman Numeral Converter handle very large numbers with overlines?

No. It focuses on the common standard up to 3999 without extended notation like overlines.