transition from bottle to cup?

Yu
What's a good time/ process to transition from bottle to cup? I heard that introducing a sippy cup with solids was a good idea but my 9 mo refuses to drink water from it.  He still gets formula from the bottle every 4-5 hours during the day. 
Should I give him formula in the sippy cup? Should I try the weighed straw cups instead? Is it too early to transition?!?!? 
Any suggestions are appreciated!! Tia

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