How much engine oil do you pour?

I have a Focus ZX3 (2003) US. In changing the engine oil myself, I am confused at the amount of new engine oil that I need to fill in. Is it 4 qts of 4.5
qts that I need to pour in? I wait the old oil to drain for about 15 minutes.
When I filled up 4.5 qts over the thanksgiving, I seem to be getting worse mileage of 30 mpg now (used to be 33-34 mpg). The dip stick reads the engine oil at top mark with 4.5 qts and the lower mark with 4.0qts.
TIA Donglok Kim
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On Mon, 12 Dec 2005 20:10:41 +0000 (UTC), Canna Service User

In my 2005 ZX4 I use 5-qts when I change the filter with the oil, which is every time I change the oil.
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