Estimate how much fuel a trip will use and what it will cost. Enter the distance, your vehicle's efficiency (mpg, L/100 km, km/L, or liters per mile), and the pump price per gallon or liter. A comparison table shows the same trip at other efficiencies in the unit you chose.
Formula
Distance is converted with the international mile and US gallon:
1 mile = 1.609344 km
1 US gallon = 3.785411784 L
Fuel in liters depends on the efficiency unit (d_mi and d_km are the trip in miles and kilometers):
mpg: L = (d_mi ÷ mpg) × 3.785411784
L/100 km: L = d_km × (L/100 km) ÷ 100
km/L: L = d_km ÷ (km/L)
L/mi: L = d_mi × (L/mi)
If the price is per gallon, divide liters by 3.785411784 to get gallons; otherwise keep liters. Cost is that volume times the pump price.
fuel amount = liters (price per liter)
= liters ÷ 3.785411784 (price per gallon)
cost = fuel amount × price
Mix units freely — kilometers with mpg, or miles with L/100 km. The calculator converts the trip before applying the efficiency formula.
Ways to spend less on fuel
Fuel is one of the larger operating costs of a car. The volume you buy is distance divided by efficiency, so anything that shortens the trip or raises efficiency lowers the bill.
Skip the car when you can. Walking, cycling, and public transit use little or no fuel per passenger. Shared buses and trains spread the energy cost across many riders; in some cities the fare is subsidized or free.
Share the ride. Two people in one car still use less fuel than two cars on the same route. Extra weight raises consumption only slightly compared with a second engine.
Drive a vehicle that matches the job. A small sedan can use about half the fuel of a large SUV on the same commute. Spare cylinders and roof boxes add drag and cost you at the pump unless you need the capability every day.
Keep the engine and tires in spec. A neglected tune or a failed oxygen sensor can waste a large share of each tank. Tires that are even a few PSI low raise rolling resistance; check them monthly, cold, at the pressure on the door placard (not the sidewall maximum). The recommended oil grade, especially one marked energy-conserving, also trims consumption a little.
Plan the route. Steady highway speed is usually more efficient than stop-and-go streets. Park once and walk between nearby stops instead of restarting the engine for each errand.
What moves the pump price
Retail gasoline and diesel track crude oil, refining, distribution, and tax.
| Factor | Why it shows up at the pump |
|---|---|
| Tax and subsidy | Excise taxes raise the retail price; subsidies can hold it down. |
| Crude markets | Brent and WTI (US$ per barrel) set the wholesale floor. |
| Policy and conflict | Embargoes, wars, and climate rules change supply and cost. |
| Geography | Regions near production are cheaper to supply than remote islands. |
| Weather and disasters | Storms and quakes can shut refineries or block deliveries. |
Examples
500 miles at 25 mpg and $3 per gallon
Fuel needed is 500 ÷ 25 = 20 gallons. At $3 per gallon the trip costs $60. The comparison table at 20 mpg would show 25 gallons and $75; at 30 mpg, about 16.67 gallons and $50.
100 km at 8 L/100 km and $1.50 per liter
Liters used are 100 × 8 ÷ 100 = 8 liters. At $1.50 per liter the trip costs $12. The same distance at 5 L/100 km would use 5 liters and cost $7.50.
Mixed units, 500 km at 25 mpg
500 km is 500 ÷ 1.609344 ≈ 310.69 miles. Gallons used are 310.69 ÷ 25 ≈ 12.43 gallons. At $3 per gallon the cost is about $37.28.