Roman Nums : Converter provides an easy way of converting Roman numerals into more understandable numbers and vice versa. Use it when you cannot quite work out the age of a building or to resolve disputes about the year in which a TV programme was made.
To use it just choose whether you want to convert from Roman numerals or from Arabic numerals and then type in the year and the corresponding value will appear. There are preferences for choosing how large numbers appear, enabling autocorrection and for choosing which order the roman numerals appear in on the keyboard.
There is a support page here that answers some common questions that you might have with the app.
Historically there have been multiple ways of writing numbers larger than 4000. The number 5000 can be written as v̅ (with a bar on top), as IↃↃ, or even V M. In this version of Roman Numerals, large numbers will automatically appear with a bar over them, but can also can be written as IↃↃ if you choose to enable them in the settings.