Roman Numeral Converter
Convert between ordinary numbers and Roman numerals, in either direction, live as you type.
Number to Roman
Roman to Number
Private by design. This page has no backend. All conversion happens in JavaScript on your own device.
How it works
The symbols
Roman numerals use seven letters: I (1), V (5),
X (10), L (50), C (100), D (500)
and M (1000). Numbers are written from largest to smallest value.
Subtractive notation
To keep numerals short, a smaller symbol placed before a larger one subtracts from
it. So IV is 4 (5 − 1), IX is 9, XL is 40 and
CM is 900. Only the pairs I, X and C before V/X/L/C/D/M are used.
The range
Standard classic numerals run from 1 to 3999, where the biggest value
MMMCMXCIX is written with four Ms. Larger values have no
single universally accepted form, so numbers outside this range are rejected rather
than guessed at.
Validation
On the Roman side, anything that is not a plausible numeral — a symbol like
IIII (repeated four times) or out-of-order letters — is rejected with a
message. The converter accepts lower-case input and normalises it, because cheque
stubs and clocks rarely worry about capitals.
How to use the Roman Numeral Converter
- Type a number to convert it to Roman numerals, or type a Roman numeral to convert it back.
- The opposite field updates live as you type.
- Copy the result.
Frequently asked questions
What range is supported?
The classic range of 1 to 3999, which covers standard Roman numerals.
Why does it use IV rather than IIII?
It uses the standard subtractive form; clock faces sometimes use IIII, but that is a stylistic exception.
Can it convert in both directions?
Yes. Entering a number gives the numeral, and entering a numeral gives the number.