To be considered a whale, it is necessary to have from 1000 to 10,000 bitcoins.
it is not that simple. there is two parts about being a whale: 1. having a lot of money 2. knowing how to use it.
the second part is complicated so I won't get into it, just know that simply being rich doesn't mean they can become whales and be effective in a market.
about #1 you should know that there is no fixed number here, having a lot of money is a relative concept. you may say 1000
BTC makes someone a whale in bitcoin market and also having 0.1
BTC makes someone a whale in some altcoin's market. it depends on the size of the market which is mostly visible in form of daily volume and on orderbooks and size of orders in it. you can simply manipulate price of some altcoins with 0.1
BTC while even having 1000
BTC may not help you change anything about bitcoin price.