Have a look in the handbook - under technical data for the engine - also gives the number of litres for a change.
You don't say how old yours is and there are different grades for the various diesels so best to check against your own manual (e.g. if yours has a diesel particle filter - DPF - like my e280CDI then you need the low ash stuff that costs the same as liquid gold).
If two grades are listed, then usually the .3x is the normal life (9,500 ish miles) and the .5x is the "extended drain" to give 12,500 miles ish.
Service interval for both will vary based on your driving style etc under Assyst.