Roman Numeral Converter
Enter a number or Roman numeral. The converter detects the direction and checks the notation.
- Roman groups
- Place values
One input, both conversion directions
Enter a whole number such as 2026 to get MMXXVI, or enter a Roman numeral such as XLII to get 42. Correctly grouped commas and lowercase letters are accepted and disclosed; mixed digits and letters, internal spaces, decimals, signs, and malformed grouping are rejected rather than guessed.
How modern Roman numeral groups work
The seven basic symbols are I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1,000. Common modern notation normally writes larger values first and uses six subtractive pairs: IV, IX, XL, XC, CD, and CM. The result card shows both Roman groups and matching place values.
Nonstandard input stays visible
A loose subtraction parser can assign a value to forms such as IIII, IL, or IIV, but that does not make them the common modern form. ToolNeko keeps the original input visible, states the interpretation rule, displays the canonical alternative, and waits for you to choose Use modern form before enabling a successful copy.
Numbers above 3,999 and overlines
This tool supports values through 3,999,999 using an overline convention in which an overlined symbol is multiplied by 1,000. Because plain text has no reliable cross-platform overline key, copied results use an underscore before each overlined symbol: _V for 5,000 and _I_V for 4,000. Historical large-number systems varied; this is a practical converter convention, not a claim that every source used one notation.
Dates and mixed batches
Date mode converts an explicitly chosen date and order to Roman components, avoiding ambiguous reverse parsing. Batch mode handles up to 100 number or Roman-numeral lines in either direction, preserves original line numbers, and shows every valid row or error. Copy all is intentionally all-or-nothing.
Local calculation and Unicode input
All conversion happens in your browser, and input values are not attached to analytics events. Unicode compatibility characters such as Ⅹ and Ⅳ are normalized to ordinary Latin-letter sequences for calculation and copying, following Unicode's guidance to prefer regular Latin letters for ordinary Roman numeral text.
Frequently asked questions
How do I convert a number to Roman numerals?
Split the number into place values, then replace each place with its common modern Roman form. For example, 1,984 becomes 1,000 + 900 + 50 + 30 + 4, or M + CM + L + XXX + IV, which combines to MCMLXXXIV.
Can Roman numerals represent zero or negative numbers?
Not in the convention used by this converter. It accepts positive whole numbers only and reports a clear error for zero, negative numbers, decimals, or exponent notation.
Why does the converter correct IIII or IC?
Historical inscriptions and clock faces can use variant forms, so the page does not claim there was one universal historical standard. For consistent modern conversion, it interprets the symbols, explains the reading, and offers the common canonical form such as IV or XCIX without silently replacing your input.
How do I type Roman numerals over 3,999?
Prefix every overlined symbol with an underscore. For example, _V represents an overlined V, or 5,000, and _I_V represents overlined IV, or 4,000. The copied result keeps this plain-text notation.
Can I convert a date to Roman numerals?
Yes. Choose a date, explicitly select month-day-year, day-month-year, or year-month-day order, and select /, -, or . as the separator. The converter handles date to Roman numerals only so a pasted Roman date is never interpreted with an unstated order.
Can I convert several values at once?
Yes. Batch mode accepts up to 100 non-empty lines and automatically detects the direction on each line. Valid rows and errors keep their original line numbers; Copy all stays disabled until every row is valid.