I've done 30 miles on 0 range before and put in 35 litres to refill.
At the end of my working day, I have a 70 mile drive home, mainly motorway, if the range is under 100 miles, I will refill before I start the trek home. However if it shows 110 miles, it will frequently drop to 0 before I get home, mainly due to the motorway/dual carriageway combination of fast roads and roundabouts, so more slowing and accelerating than had it been one long road without roundabouts.