Roman numerals
From 1 to 3999 in Roman numerals, and back.
On this device: nothing is uploaded.
How it works
Type a number from 1 to 3999 or a Roman numeral. Reading Roman numerals only accepts the canonical spelling (IV, not IIII), so “VX” is rejected rather than guessed.
FAQ
Why only up to 3999?
The standard system has M as its largest symbol and repeats it at most three times.