Convert numbers to Roman numerals and back, with strict validation that rejects malformed numerals like IIII and IC. Free, runs in your browser.
First time here? Pick a direction — number to Roman, or Roman to number Your input is processed locally and disappears when you close the tab.
Roman numerals turn up in film credits, book chapters, monarch names, and the cornerstones of buildings, and almost nobody reads MCMXCIV at a glance. This free Roman numeral converter handles both directions instantly.\n\nThe part that separates a good converter from a careless one is validation. Adding up letters will happily turn IIII into 4 and IC into 99, but neither is a valid numeral — four is IV and ninety-nine is XCIX. This tool checks a numeral by regenerating it from the value it parsed and confirming the two match, which rejects every malformed form without maintaining a list of exceptions.\n\nReference charts for the seven symbols and the six legal subtractive pairs sit below the converter, because the rule people forget is that subtraction only works in those six combinations. A symbol can be subtracted from the next one or two sizes up, and no further.\n\nThe range is 1 to 3,999, which is the limit of standard notation — there is no zero, no negatives, and larger values need an overbar with no agreed text form. Everything runs in your browser. Pair it with the Number to Words converter for written amounts, or the Number Base Converter for binary and hexadecimal.
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A smaller symbol before a larger one subtracts. Only these six pairs are valid, which is why IC is not 99 — you write XCIX.
Converting a numeral checks it is genuinely well-formed rather than just adding up the letters, so malformed input is rejected instead of silently producing a number.