When I ran mine out, it took 44 litres to refill it not 33.I have a Sandero Stepway BI Fuel Comfort
It did inform me LPG low 30miles away it said low LPG on the info.
JUST RAN OUT OF lpg at 290 miles on Stepway thats good on 33 litres.
When I refilled at the "LPG low" warning it took just 32 or 33.
Checked the manual, the LPG tank capacity is "approx 40 litres" useable.