This answers a different question from a cost calculator: not what the fuel costs but whether you have enough of it. The volume needed is the distance multiplied by the consumption rate, but the useful output is the comparison against what is in the tank right now. From that comes the distance you can cover before the first stop and the number of refills the route actually demands.
Consumption here is litres per 100 kilometres, the standard metric measure, because it scales linearly with distance in a way miles per gallon does not. If your car reads in mpg imperial, divide 282.481 by it — that constant is 100 x 4.54609 / 1.609344, the litres in a gallon over the kilometres in a mile. Fifty mpg imperial is 5.65 litres per 100 km.
A 450 km route at 6.5 L/100 km needs 29.25 litres. A 50 litre tank gives a theoretical range of 769 km, but starting at 80 per cent and refusing to drop below a 5 litre reserve leaves 35.0 usable litres, or 538 km before the first stop. Manufacturer tank capacities usually include a couple of unusable litres, so a reserve is sensible rather than timid.
The formula
distance- Route length in kilometres or miles
consumption- Litres per 100 km, real-world rather than brochure
tank- Usable tank capacity in litres
reserve- Litres you refuse to go below
How to use this calculator
- Enter the route distance and choose kilometres or miles.
- Enter your real-world consumption in litres per 100 km.
- Enter the tank size and how full it is right now.
- Set the reserve you want to keep, then read the litres needed and the stops required.
Worked examples
450 km at 6.5 L/100 km
The route needs 29.25 litres. A 50 litre tank has a full range of 769 km, and starting 80 per cent full with a 5 litre reserve gives 35.0 usable litres — 538 km, which covers the route with 10.8 litres to spare.
The same route in a thirstier vehicle
A loaded van at 11 L/100 km needs 49.50 litres for the same 450 km. With the same 35.0 usable litres on board it would run dry after 318 km, so one refuelling stop becomes compulsory.
How to read your score
Frequently asked questions
How do I convert my mpg figure into litres per 100 km?
Divide 282.481 by your miles per imperial gallon. The constant is 100 x 4.54609 / 1.609344. For American figures use 235.215 instead, because a US gallon is 3.785411784 litres rather than an imperial one.
Why keep a reserve at all?
Quoted tank capacity is usually a fill-to-the-neck figure, and the pickup sits slightly above the floor of the tank, so the last litre or two is not reliably available. Running to the very bottom also stirs up whatever sediment has settled and, on some cars, runs the in-tank fuel pump hot.
Does a full tank make the car heavier and less efficient?
Marginally. Fifty litres of petrol weighs about 37 kg, which is under three per cent of a typical family car and worth well under one per cent in consumption. It is not a reason to run half-empty.
Should I use the brochure consumption figure?
No. WLTP figures are measured on a rolling road with a specific cycle and are typically 10 to 20 per cent better than what drivers see in mixed use. Measure your own over a few tanks and use that.
Does towing change the number much?
Substantially. A caravan or loaded trailer commonly adds 30 to 50 per cent to consumption because of the extra frontal area and mass. Raise the consumption input accordingly rather than trusting the solo figure.
Trip fuel reference
| Distance | 5 L/100km | 6 L/100km | 7 L/100km | 8 L/100km | 11 L/100km |
|---|---|---|---|---|---|
| 100 km | 5.0 L | 6.0 L | 7.0 L | 8.0 L | 11.0 L |
| 200 km | 10.0 L | 12.0 L | 14.0 L | 16.0 L | 22.0 L |
| 300 km | 15.0 L | 18.0 L | 21.0 L | 24.0 L | 33.0 L |
| 500 km | 25.0 L | 30.0 L | 35.0 L | 40.0 L | 55.0 L |
| 800 km | 40.0 L | 48.0 L | 56.0 L | 64.0 L | 88.0 L |
| 1000 km | 50.0 L | 60.0 L | 70.0 L | 80.0 L | 110.0 L |
| 1500 km | 75.0 L | 90.0 L | 105.0 L | 120.0 L | 165.0 L |
For reference, 5.65 L/100 km is 50 mpg imperial and 9.42 L/100 km is 30 mpg imperial.