Convert whole numbers to standard Roman numerals and Roman numerals back to Arabic values. Validate subtractive notation, see how each symbol contributes, and compare the compact standard form with its fully additive equivalent.
Step by step
01Choose the direction
Start with an Arabic whole number or a sequence of Roman symbols.
02Enter a value
Standard notation covers 1 through 3,999 using I, V, X, L, C, D, and M.
03Check the breakdown
Read each ordinary symbol or subtractive pair and the value it contributes to the total.
04Compare standard and additive forms
The standard form is shortest; the additive form makes every repeated value explicit.
Worked example
Given
Break the numeral into values
M = 1000
CM = 900
XC = 90
IV = 4
────────────
total = 1994A smaller symbol before a permitted larger symbol subtracts: CM is 900, XC is 90, and IV is 4. Everything else adds from left to right.
Why this one
Only six subtractive pairs are standard
I precedes V or X, X precedes L or C, and C precedes D or M. Forms such as IL for 49 are non-standard.
Five-symbols do not repeat
V, L, and D appear once at most; I, X, C, and M ordinarily repeat no more than three times in a row.
Roman notation has no ordinary zero
The classical system was built for recording positive quantities, not positional arithmetic with a zero digit.
The common standard stops at 3,999
Larger values require conventions such as overlines that are not consistently representable in plain text.
The judgement call
4
IV
I may subtract from V.
9
IX
I may subtract from X.
49
XLIX
Each place is encoded separately: 40 plus 9.
49 written IL
Non-standard
I cannot subtract from L across place values.
Reference
FAQ
Symbols usually add from left to right. In six standard pairs, a smaller symbol before a larger one subtracts, such as IV = 4 and CM = 900.
There is no standard classical Roman numeral for zero, so this converter begins at one.
MMMCMXCIX represents 3,999. Larger numbers need an added convention such as an overline for thousands.
Standard notation encodes each decimal place separately: 40 is XL and 9 is IX. I is only allowed before V or X.
The symbols are conventionally uppercase. The converter can normalize typed lowercase letters, then validates the resulting standard form.
Conversion and validation happen entirely in your browser.
Keep going
Number Base Converter
Compare positional representations from binary to base 36.
Prime Number Checker
Inspect the arithmetic properties of the converted value.
Number Rounding Tool
Format modern decimal quantities consistently.
GCD & LCM Calculator
Explore divisors and multiples of the converted value.