ATS Calculators
Romans

In the movies the years are often printed with old Roman numbers. 
Here is a converter for you. Calculator, itself, does not have any limitations.

Ancient - Converter
Rom number Calculate
Common number Calculate

 

Conversions

  Rom Arabic  
Thousand M 1000

Romans didn't have negative numbers. The scale of numbers ended to 1000. A single Arabic number consisted from 1 to three letters. A single number was read from left to right. When there is  smaller number before bigger number it reduces the value of the number. And when there is a smaller number after big number it increases the value. The converter does not have any limitations. It implements the ancient Roman formula. It can also convert Roman numbers, which were presented incorrectly ( like IICIIX ) and so on 
Five hundred D 500
Hundred C 100
Fifty L  50
Ten X 10
Five V 5
One I  1
Sample from the numbers

VI = 6 ( 5 + 1 )
IX = 9 ( 10 - 1 )
MCMXXCI =  1981

MCM = 1900 ( 1000 + 1000 - 100 )
XXC = 80 ( 100 - 10 - 10 )
I = 1
From these come
MCM + XXC + I =  MCMXXCI