Quick answer
Roman numerals use I, V, X, L, C, D and M with subtractive pairs IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900. 1994 is MCMXCIV (1000 + 900 + 90 + 4).
Choose a direction, then enter a number from 1 to 3,999 or a Roman numeral. The calculator converts it and rejects non-standard forms.
Related tools: Random Number Generator: Random integers in a range, optionally repeatable with a seed. Scientific Calculator: Evaluate expressions with functions, constants, powers and factorials. Prime Number Calculator: Check whether a number is prime and find the next prime.
How to use the Roman Numeral Converter
- Choose convert: Number → Roman and Roman → Number.
- Type value, for example 1994 or MCMXCIV.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Convert | Choose one: Number → Roman; Roman → Number | Starts at Number → Roman |
| Value | Text, such as 1994 or MCMXCIV | — |
Formula and method
Formula
Subtractive notation: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900
IEEE-754 double precision; shown to at most 6 decimal places.
Greedy symbol subtraction; Roman input is validated by converting back and comparing.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Convert = Number → Roman; Value = 1994.
| Result | Value |
|---|---|
| Roman numeral | MCMXCIV |
Example 2
Inputs: Convert = Roman → Number; Value = XLII.
| Result | Value |
|---|---|
| Number | 42 |
Example 3
Inputs: Convert = Number → Roman; Value = 3999.
| Result | Value |
|---|---|
| Roman numeral | MMMCMXCIX |
The first line is the headline result (roman numeral). IEEE-754 double precision; shown to at most 6 decimal places.
Building a numeral
Take the largest value that fits, write its symbol and subtract it, repeating until zero. For 1994: M (1000) leaves 994; CM (900) leaves 94; XC (90) leaves 4; IV (4). A symbol repeats at most three times, so 4 is IV rather than IIII.
Range
Standard numerals stop at 3,999 (MMMCMXCIX). Larger numbers need an overline (vinculum) to multiply by 1,000, which this tool does not use. Entries such as IIII are rejected rather than guessed.
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Value: entering "4000" shows "Enter a whole number from 1 to 3999." beside that field and no result.
Choosing between the Roman Numeral Converter and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Random Number Generator](/math/random-number-generator/) | minimum, maximum and how many | Random numbers |
| [Scientific Calculator](/math/scientific-calculator/) | expression and angle mode | Result |
| [Prime Number Calculator](/math/prime-number-calculator/) | number | Result |
| [Fibonacci Sequence Calculator](/math/fibonacci-sequence-calculator/) | position n | F(10) |
| [Factorial Calculator](/math/factorial-calculator/) | n | n! |
Assumptions and limitations
- Range 1–3999
- Non-canonical forms such as IIII are rejected
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for value to confirm this.
Frequently asked questions
What is 2025 in Roman numerals?
2025 is MMXXV: MM is 2000, XX is 20 and V is 5.
Why is there no zero?
The system had no symbol for zero.
Can I write a date?
Convert day, month and year separately.
What does the Roman Numeral Converter calculate?
Convert between numbers and Roman numerals (1–3999). It returns Roman numeral.
What formula does the Roman Numeral Converter use?
Subtractive notation: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900. Greedy symbol subtraction; Roman input is validated by converting back and comparing.
What do I need to enter in the roman Numeral Converter?
You enter Convert and Value.
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Range 1–3999.
What are the limits of this converter?
Range 1–3999. Non-canonical forms such as IIII are rejected.
What does the “Convert” option change?
It sets how the roman Numeral is worked out. The choices are Number → Roman and Roman → Number.
What is an example of a roman Numeral result?
With convert Number → Roman and value 1994, the roman numeral is MCMXCIV.
Related calculators
- Random Number Generator — Random integers in a range, optionally repeatable with a seed.
- Scientific Calculator — Evaluate expressions with functions, constants, powers and factorials.
- Prime Number Calculator — Check whether a number is prime and find the next prime.
- Fibonacci Sequence Calculator — The nth Fibonacci number and the sequence leading to it.
- Factorial Calculator — n! computed exactly.
- Complex Number Calculator — Add, subtract, multiply and divide complex numbers.
Sources
- OpenStax, Algebra and Trigonometry 2e (Rice University): exponents, radicals, logarithms and inverse trigonometric functions
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.