Glossary
Tankful (Full Tank)
Direct Answer / TL;DR
What is Tankful (Full Tank)?
The amount of fuel needed to fill a vehicle's tank from its current level to maximum capacity. The fill amount is a critical input in the detour calculation — the more you fill, the bigger the gross saving from a cheaper price per litre, and the further it's worth driving.
Why does it matter for UK drivers?
UK petrol car tank sizes typically range from 40 litres (small city cars like Fiat 500) to 70 litres (large SUVs and estates). The average UK car has a tank capacity of approximately 55 litres, and drivers typically fill to 70–80% capacity in practice — so a typical fill is 40–50 litres.
The fill volume matters enormously in the detour calculation. Gross saving = price difference per litre × litres filled. If you fill 30 litres, a 5p/L saving gives £1.50 gross — not much to drive for. If you fill 60 litres, the same 5p saving gives £3.00 — more meaningful, and a longer detour is justified.
WorthThePump asks for your fill amount rather than tank capacity because most people don't fill to the brim every time. Partial fills (20–30L) are common in urban driving where the weight of a full tank is a minor concern. The fill amount input should reflect what you're actually planning to put in.
A 'fill it up' scenario (full tank from empty) produces the largest gross saving and the most favourable break-even distance. For a driver with a 60-litre tank filling up completely at a 5p/L saving, the gross saving is £3.00 — enough to justify a detour of 2–3 miles in most vehicles.
WorthThePump allows you to specify the fill amount in pounds sterling (how much you're planning to spend) because most UK drivers think in terms of 'I'm putting in £50 worth' rather than '45 litres'. The pound amount is converted to litres using the cheapest station's price to determine the fill volume for the calculation.
Related terms
Further reading
Now you know what Tankful (Full Tank) means —
find out if your nearest cheap station is actually worth the trip.