like nathan said, capacity is 6 quarts. you're never getting all 6 quarts out, so you won't be putting all six quarts back in.
and you're treating the dipstick like the hand of God. it's a rough estimate at best, and is dependent on so many factors.
-is your car 100% level?
-what's the true capacity of your filter?
-what temp is the oil at?
-what viscosity oil?
take out your drain plug and filter and get as much of the old oil out as you can in a REASONABLE amount of time (4 hours? wish i had that kind of time). fill it with about 5.5 quarts, run it, kill it, check it again after a while. probably add a little. done.
sill unsure? check it when you buy gas.
(but wait - i went for gas when the gauge said 'empty' and the miles remaining said '0' - but when i filled the tank it only took 15.25 gallons, and i know the capacity is 16 per the manual, and... and...)