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Travel"How far can I make it?" is the road trip question that matters. The math is multiplication you can do in your head — but the honest answer subtracts a reserve, because driving on fumes is how people end up walking.
Here's the range formula, what your fuel light really means, and the driving habits that stretch a tank the farthest.
Try it yourself: Price the trip too — fuel cost per mile and per journey. Fuel Cost Calculator →
The range formula
Range = tank capacity × fuel economy
— e.g. 13 gal × 32 MPG = 416 miles —
— e.g. 13 gal × 32 MPG = 416 miles —
Your tank capacity is in the owner's manual (or on the fuel door sticker). Use your real economy, not the sticker figure — check your trip computer's average over a few tanks, or compute it from fill-ups.
Always subtract a reserve
Plan fuel stops at 85–90% of theoretical range. That 416-mile tank means planning stops by ~370 miles. Reasons:
- The fuel light lies (a little). Most cars trigger it with 1–2 gallons left — roughly 30–60 miles — but the exact reserve varies by model and the gauge isn't precise.
- Running dry damages modern cars. The fuel pump is cooled by the fuel itself; running empty can overheat it, and sediment at the tank bottom can clog the filter.
- Conditions change. Headwinds, mountains, traffic, and detours all eat range you counted on.
EVs: same math, different units
Range = battery capacity (kWh) × efficiency (miles/kWh). A 75 kWh battery at 3.5 mi/kWh = ~263 miles. Same reserve logic applies — EV drivers plan around 10–20% remaining, since chargers (unlike gas stations) aren't on every corner yet.
Stretching a tank
- Slow down. Aerodynamic drag rises with the square of speed — dropping from 75 to 65 mph can improve economy 10–15% on the highway.
- Check tire pressure. Under-inflated tires measurably increase rolling resistance; the correct pressure is on the driver's door jamb.
- Ease off the AC at low speeds (open windows instead), but use AC on the highway — open windows at speed create more drag than the AC costs.
- Drive smoothly. Gentle acceleration and coasting to stops beat jackrabbit starts by a wide margin in city driving.
Planning a long trip: a worked example
Denver to Kansas City is ~600 miles. Your car: 14-gallon tank, 30 MPG real-world = 420-mile theoretical range. Plan stops at ~370 miles: one fuel stop around the 350-mile mark gets you there with reserve to spare. Total fuel: 600 ÷ 30 = 20 gallons. At $3.20/gal that's $64 — and you now know exactly one stop is enough, so no anxious gas-station math at midnight in western Kansas.
What affects range most
- Speed. The single biggest highway factor — drag squares with speed.
- Load and roof cargo. A roof box can cut highway economy 10–25%; pack inside when possible.
- Cold weather. Winter blends, warm-up idling, and denser air routinely cost 10–15%.
- Tires. Under-inflation and aggressive tread both add rolling resistance.
Trucks and motorcycles
The formula doesn't change, but the numbers do: a full-size pickup might do 18 MPG on a 26-gallon tank (468 miles), while a motorcycle might do 55 MPG on 4 gallons (220 miles). Small tanks mean frequent stops regardless of efficiency — plan by range, not by MPG alone.
Diesel drivers: one more variable
Diesel contains ~10–15% more energy per gallon than gasoline, which is why diesel cars post better economy figures. But diesel fuel often costs more per gallon — so compare on cost per mile, not MPG. A diesel doing 40 MPG on $4.00/gal fuel costs the same per mile as a gas car doing 35 MPG on $3.50/gal.
Frequently asked questions
Typically 30–60 miles (1–2 gallons), but it varies widely by model — some cars give you 80+, others barely 25. Check your owner's manual once and remember your car's number.
Yes. The fuel pump relies on gasoline for cooling and lubrication, and the dregs can carry sediment into the filter. Habitually running near-empty shortens pump life.
It adds roughly 5–10% to consumption. Below ~40 mph, open windows are more efficient; above that, closed windows + AC wins because of aerodynamic drag.
Sticker figures come from lab test cycles. Real driving — short trips, cold starts, traffic, speed, AC — typically returns 10–30% less. Use your own measured average for planning.
Disclaimer: Range estimates depend on driving conditions, load, weather, and vehicle condition. Always keep a fuel reserve and know your vehicle's actual low-fuel behavior.