Roman Numeral Converter
Convert numbers to Roman numerals and back, from 1 to 3999. Nothing is uploaded - the conversion runs locally.
How Roman numeral conversion works
A tiny lookup table drives the conversion: starting from 1000 = M and 900 = CM down to 1 = I, the tool subtracts the largest value that still fits. That greedy pass produces the standard subtractive form, so four is IV and not IIII, and 1776 is MDCCLXXVI. Reading a Roman numeral works the other way: each symbol is compared with the next, and a smaller value before a larger one is subtracted. Anything that is not canonical, such as IIII or VC, is rejected and the correct form is shown. Values above 3999 need overline notation and are outside the scope of this page. Neighbouring tools include the text case converter and the word counter.
Frequently asked questions
Which numbers are supported?
Whole numbers from 1 to 3999 in standard subtractive notation. Values above 3999 need overline (vinculum) notation, which this tool does not implement.
What is subtractive notation?
Instead of writing four identical symbols, a smaller symbol before a larger one subtracts, so four is IV and not IIII, and nine is IX and not VIIII.
Why is there no zero?
Roman numerals have no symbol for zero, so the range starts at one; entering zero or a negative number is rejected with a clear message.
How are invalid strings treated?
A string that uses only valid letters but breaks the ordering rules, such as IIII or VC, is rejected and the standard form of the intended value is shown instead.
Does it convert both directions?
Yes. Enter a number to get the Roman form, or enter a Roman numeral to get the number; the two fields stay independent so you can convert either way.
Is the conversion done locally?
Yes. The conversion uses a small lookup table in your browser; nothing is sent to a server.
Related: change letter casing with the text case converter, count the draft with the word counter, order a list with the line sorter, format data with the JSON formatter, and browse every browser-only tool on the all tools page.