there isn't really a set amount for being a whale since the whale is not an exact explanation. and i think it differs from market to market. but basically you can call anybody who has deep pocket and can control the market price if he whishes.
can be 1000BTC
or can be 10,000,000 [put altcoin name here]
And in relation to the distribution of BTC.
Get it ?
BTC top holders are rare.. people who have a super small amount are common.
So even though a super small BTC holder *may* be able to control a super small ALT market
i don't think that makes him a true whale.. more of a pseudo-whale of sorts LOL
I would think we have to attribute some rarity to the term "Whale"
In other words we all can't be whales.
Most of us have at times been able to control an entire market (on a coin nearly dead for example)
It often does not take much at all..
Would most of us be considered Whales then ?
no.
"It's relative" is a good reply but i think the distribution of BTC itself is key too.
Who has how much etc..
EDIT:I would NOT specify an exact amount / limits etc.