there are many very good jewellers in the medina in sousse tell him to go there and i am sure they will have a conversion chart as caley has said.... if they even convert it into french sizing if thats not what they already use, then you can convert it on the internet. most likely it will be french sizing as clothes etc are in european sizing so tell him to go to the medina get a real sizing, obv not too tight and tell him to ask the jeweller to tell him what size he is in french. many jewellers in the medina will be able to do this no problem.