As of market close on 6/17, a simple market cap weighted version of $ETF would look something like this:  $AMZN: $1.32t + $MSFT: $1.49t + $AAPL: $1.53t = $4.43t total  $AMZN: 1.32/4.43 = .30 $MSFT: 1.49/4.43 = .33 $AAPL: 1.53/4.43 = .35  This is how funds like $SPY and $QQQ work.