Roman numeral converter — both directions
Convert numbers to Roman numerals and back. Invalid forms like IIII and IC are rejected rather than quietly accepted.
Runs entirely in your browser — nothing is uploaded.
Symbol values
Roman numerals have no zero and no standard way to write above 3,999 without overbars, which is why the range stops there. Invalid forms such as IIII and IC are rejected rather than silently accepted.
How to use
- Pick a direction. Number to numeral, or numeral to number.
- Type your value. Numerals are case-insensitive.
- Check the symbol table. The seven letters and their values are listed below.
Questions
How does subtractive notation work?
A smaller value before a larger one is subtracted: IV is 4, IX is 9, XL is 40, CM is 900. Only I, X and C are used this way, and only before the next two higher symbols — so 99 is XCIX, never IC.
Why is 4 not IIII?
Standard notation never repeats a symbol four times; IV is correct. IIII does appear on some clock faces for visual balance, but it is not valid in the standard system, so this tool rejects it.
Why stop at 3,999?
Because 4,000 would need MMMM, which breaks the no-four-repeats rule. Larger numbers historically used an overbar to multiply by a thousand, a convention with no standard plain-text form.
Is there a Roman zero?
No. The system has no symbol for zero and no concept of it as a number — one reason Roman arithmetic was so much harder than the positional system that replaced it.