I mixed 2 gallons of Dupont acrylic lacquer for My truck...
It was definitely more than I needed, but what if I needed paint
for a mishap later...Its also important that You box all Your paint together in one container...That way if You ever need paint
later You won't have problems with a mismatch...
I also used clear, but clear has no strength when sprayed
alone, so I added a quart of color to the clear which gives it the strength it needs to cross-link...
I know You are talking a single stage urethane, so I would
recommend purchasing 2 gallons knowing it will be more than needed, but You can bank the rest for down the road.. Bill B