Complete guide
Roman numeral converter and canonical form checker
Choose a direction and enter a decimal integer or Roman numeral. Calculator24 converts it, shows the symbol breakdown and rejects noncanonical forms such as IIII or IC.
Roman numeral symbols
Seven Latin letters carry the common values I, V, X, L, C, D and M. Values usually descend and are added.
Subtractive pairs
Six standard pairs place a smaller value before a larger one: IV, IX, XL, XC, CD and CM. The converter emits only canonical modern forms.
Convert decimal to Roman
Take the largest available symbol or pair repeatedly and subtract its value until the remainder is zero.
Convert Roman to decimal
Read recognized tokens from left to right and add their values. The result is converted back to Roman to ensure the input was canonical.
Range and typography
This tool supports 1–3,999 using ordinary Latin letters. Unicode recommends composing Roman numerals from Latin letters for most purposes; larger historical forms require separate conventions.
Roman numeral values
| Token | Value | Token | Value |
|---|---|---|---|
| M | 1000 | CM | 900 |
| D | 500 | CD | 400 |
| C | 100 | XC | 90 |
| L | 50 | XL | 40 |
| X | 10 | IX | 9 |
| V | 5 | IV | 4 |
| I | 1 | — | — |
Frequently asked questions
What does MCMXCIV equal?
It equals 1,994.
Why is 4 written IV?
I before V subtracts one from five.
Is IIII accepted?
This converter requires the common canonical form IV.
Can Roman numerals represent zero?
The classical system used here has no zero symbol.
Why is the maximum 3,999?
Values above it need repeated M or an extended convention such as overbars, which is not universal.
What to keep in mind
Uses the common modern canonical form for 1–3,999. Historical conventions and overbar notation vary.
Results display up to 8 decimal places; exported numbers preserve calculation precision. This is a calculation summary, not an official certificate.