Every stop OTW offers you has been checked against this number, and every stop it hides failed it. It is deliberately pessimistic in two places, because the cost of the two mistakes is not the same: being told to drive past a servo you could have reached is an annoyance, and being sent at a servo you cannot reach is a tow truck.
Cars are advertised with a combined-cycle consumption figure measured under test conditions. Real driving — hills, air conditioning, a loaded car, highway speeds, a roof box — uses more. OTW adds a flat 20% to the published figure rather than pretending the test number is what you will see. If you know your own car does better or worse than that, override the consumption on the form above and OTW will use yours instead.
OTW holds back a reserve of 10% of the tank, or 5 litres, whichever is larger, and never plans a stop that relies on it. A fuel gauge is not a precise instrument near empty, the pickup in the tank is not at the very bottom, and a headwind costs more than you would think. The reserve is what absorbs all three.
A mid-size car with a 60 litre tank, showing half full, advertised at 8.0 L/100km:
| Tank | 60 L | From the manufacturer's figure for your model, or your own override. |
| Fuel level | Half — 30 L | What you tell the slider you have now. |
| Reserve held back | 6 L | 10% of the tank, or 5 L, whichever is larger. |
| Usable fuel | 24 L | What is left to drive on. |
| Lab consumption | 8.0 L/100km | The combined-cycle figure your model is advertised with. |
| Real-world rate | 9.6 L/100km | The lab figure plus 20%. |
| Range | 250 km | 24 L at 9.6 L/100km. |
The same car on the same fuel would be quoted roughly 300 km on its lab figure with no reserve held back. The 50 km between those two numbers is the part people get stranded in.
Consumption figures come from the Commonwealth Green Vehicle Guide, which publishes the tested figures for vehicles sold in Australia. Tank capacities are not in that dataset for every model, so where one is missing OTW offers the capacities known for that make and model and asks you to pick — and you can always type your own. The exact provenance and copyright statements are in the footer of this page.
In all four cases, set the fuel level lower than you think it is. The planner will simply suggest an earlier stop.
Your car is stored in your own browser and never sent to a server. How the stop ranking works covers what happens after the range is known.