Fuel Stop Planner

How Fuel Stop Planning Works

Planning fuel stops is not “trip distance divided by tank range”. Nobody drives to empty, and the last quarter of a tank is the part you want in reserve when the exit you planned on turns out to have a closed station.

The formula this page uses:

Usable range = Full tank range × (1 − reserve fraction) Stops needed = ceiling(Trip distance ÷ Usable range) − 1 Ideal spacing = Trip distance ÷ (Stops + 1)

The “− 1” is the part people get wrong. You leave with a full tank, so a 700-mile trip in a car with 400 miles of usable range needs one stop, not two. You only stop when the tank runs out mid-route, and it never runs out at the start.

Worked example. An 800-mile drive, 400-mile tank range, refuelling at the quarter mark:

• Usable range = 400 × 0.75 = 300 miles
• Stops = ceiling(800 ÷ 300) − 1 = 3 − 1 = 2 stops
• Spacing = 800 ÷ 3 = every 267 miles

Even spacing matters more than it sounds. The naive plan is to drive 300, fill up, drive 300, fill up, then limp the last 200. That works right up until the second station is closed and you are 90 miles from the next one with a quarter tank. Spacing the stops evenly leaves the same margin at every one of them.

Why the reserve fraction is an input. A quarter tank is the usual advice and the default here, but it depends on where you are. Across the Nevada or Australian interior, running down to a quarter is optimistic and a third is more sensible. In dense suburbia with a station at every junction you can push to a tenth without drama. Set it to what the road actually looks like.

Range is not the number on the sticker. Manufacturer range figures assume steady speed on flat ground with a light load. Real range drops with a roof box, a headwind, mountains, a full car, air conditioning, and cold weather. Take 10 to 15% off the advertised figure before you enter it, and more in winter.

Electric vehicles change the arithmetic in one specific way. The stop count works identically, but the reserve should be larger (chargers are sparser and can be occupied or broken) and each stop is 30 to 45 minutes rather than five. That makes the number of stops matter far more than it does with petrol. A 200-mile usable range on an 800-mile drive is 3 stops and roughly two hours of standing around.