Generally, one bout of feeding takes in between a pint and half of a pint of blood (that's .5 to .25 liters to metric folks). A vampire's stomach can hold between 2 and 8 pints (Metric: between 1 and 4 liters) at any given time, and a vampire must feed (off of PCs or posed NPCs) at least once every few days (the 'few days' determined by the vampire's Willpower minus their Power) before they grow hungry. After that, the hungry vampire has a percent chance equal to twice their Willpower of not flipping out (like a hungry cat left alone with a canary) when thinking about or seeing blood. This drops down by 2 percent every day after the 'few days'. When the count reaches 'zero percent', the hungry vampire will effectively be a Revenant and do whatever it takes to get blood unless restrained physically or mentally.
If a vampire is trying to binge-feed for some reason, their system processes about one pint (Metric: 0.5 liter) every fifteen minutes.
SEE: +help feed
A vampire that, for some reason, decides to try to rely on mainly just Alternate Feeding is in for a rough ride. It's generally comparable to if one tried to live off of really tasty rice-cakes and water without eating anything containing the various vitamins and minerals needed to sustain one; it'll stave off the hunger, but malnutrition will eventually kick in. Oftentimes, this might manifest as a hunger for the one outlet they're allowing themselves (IE: emotion) instead of the one they need (IE: blood), thus leading to the Ardeur cited in the books if something "lusty" is the emotion they feed off of, and leading to something else if it's another emotion (EG: A desire to cause and experience widespread grief if their Alt Feed emotion is sorrow, widespread rage if their Alt Feed is anger, et cetera). This is nothing that a regular intake of fresh human blood wouldn't fix, though.