OK I think I cracked it
If anyone has a better way let me know
RTRIM(CAST(cast(round(sum(CAST(REPLACE(CAST(SUBSTRING([CONTENTS],PATINDEX('%'+'x'+'%',[CONTENTS])+2,PATINDEX('%'+'ml'+'%',[CONTENTS])-5)AS numeric),'ml','') AS numeric))/1000,0)as numeric(15,0))AS CHAR))+' Ltrs' AS K