A question about Staking Amounts

This may sound dumb, but I want to stake ETH, and I want to wait until I have enough to make it worth the time. But if you stake, lets say .5 ETH somewhere like Coinbase, and then go ahead and buy more, so that you have 1 ETH, you are only staking .5 ETH correct? You arent then staking 1.0 ETH?

Just want to make sure I understand all the finer points of anything before I really start getting down to brass tacks about the decisions I want to settle on.