How to Calculate Fuel Cost for a Trip
Planning a road trip? Knowing the fuel cost in advance helps you budget properly and choose the most economical route. Whether you use liters per 100 km or miles per gallon, the calculation takes under a minute.
The Fuel Cost Formula
Metric (L/100km):
Fuel Cost = (Distance in km ÷ 100) × Consumption (L/100km) × Price per liter Imperial (MPG):
Fuel Cost = (Distance in miles ÷ MPG) × Price per gallon The metric formula calculates how many liters you need, then multiplies by the price. The imperial formula divides distance by efficiency to get gallons needed, then multiplies by price.
Step-by-Step Guide
- Find your trip distance. Use Google Maps or a route planner. For a round trip, double the one-way distance. Include any planned detours.
- Know your vehicle's fuel consumption. Check the owner's manual, the sticker inside the fuel door, or look it up on fueleconomy.gov. Real-world consumption is typically 10-20% higher than official ratings.
- Get the current fuel price. Check GasBuddy for US prices. Prices can vary significantly along your route — highway gas stations are often pricier.
- Plug the numbers into the formula. See the worked examples below.
- Add a 10-15% buffer. Traffic, weather, A/C usage, and elevation changes all increase real consumption beyond the rated figure.
Worked Examples
Example 1: Metric (Europe)
A 500 km road trip in a car consuming 7.5 L/100km, with fuel at €1.65/L:
Liters needed = 500 ÷ 100 × 7.5 = 37.5 L
Fuel cost = 37.5 × €1.65 = €61.88
With 10% buffer ≈ €68.06
Example 2: Imperial (US)
A 310-mile trip in a car getting 31 MPG, with gas at $3.50/gal:
Gallons needed = 310 ÷ 31 = 10.0 gal
Fuel cost = 10.0 × $3.50 = $35.00
With 10% buffer ≈ $38.50
Skip the Math — Use Our Free Calculator
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Open Fuel Cost Calculator →Factors That Affect Fuel Consumption
- Driving speed: Fuel efficiency drops sharply above 65 mph (105 km/h). Maintaining highway speed limits can save 10-20% on fuel.
- Air conditioning: A/C can increase fuel use by 5-10%, especially in stop-and-go traffic. At highway speeds, A/C is more efficient than open windows.
- Tire pressure: Under-inflated tires increase rolling resistance. Check pressures before a long trip — each 1 PSI below optimal costs roughly 0.2% in fuel efficiency.
- Vehicle load: Every extra 100 lbs (45 kg) reduces fuel economy by about 1%. Roof racks and cargo boxes add aerodynamic drag, costing 2-8% more fuel at highway speed.
- Terrain: Mountainous routes consume significantly more fuel than flat highways. Estimate 20-30% more fuel for hilly terrain.
- Cold weather: Fuel economy drops 15-25% in freezing conditions due to denser air, tire stiffness, and engine warm-up cycles.
Frequently Asked Questions
What is the fuel cost formula?
For metric: Fuel Cost = (Distance in km ÷ 100) × Consumption (L/100km) × Price per liter. For imperial: Fuel Cost = (Distance in miles ÷ MPG) × Price per gallon. Both formulas give you the total fuel expense for a trip.
How to convert L/100km to MPG?
Divide 235.215 by the L/100km value. For example, 7.5 L/100km = 235.215 ÷ 7.5 ≈ 31.4 MPG. To go from MPG to L/100km, divide 235.215 by the MPG value.
Does driving speed affect fuel cost?
Yes, significantly. Most vehicles are most fuel-efficient between 45-65 mph (70-105 km/h). Driving at 80 mph instead of 65 mph can increase fuel consumption by 15-25%, adding substantial cost to longer trips.
How to calculate fuel cost for multiple stops?
Add up the distance between each stop to get the total distance. Then apply the formula once using the total distance, or calculate each leg separately if fuel prices differ by region. Remember to check prices along your route using GasBuddy or similar apps.