You do the mental calculation of gallons to litres, because you don’t want to fill up on the Canadian side of the border(despite being«energy independent» they are more expensive when it comes to gas(petrol)). You tell the friendly kid, «12 litres» — enough to get you past the border. I don’t know if full serve is the law here, like it is in New Jersey, but we figure the kid is getting paid so we don’t do the typical American thing and tip on top of that. You drive away and continue to enjoy rural Ontario.