Hello, I don't know the royal measurement system, how it converts etc.
Could we have the metric system in between brackets everywhere royal system is used ?
Here is an example : http://musicbrainz.org/edit/15973303 (metric system conversion should be both in the edit page and edit review page between brackets).

Kuno told me once that in his domain, the royal system was used for vynils even if he lives outside of UK etc.
But I can assure that, in France, very few people use this and even fewer people can convert this by themselves (even the clever type of French).