Planning a road trip or budgeting your commute? Enter your trip distance, your vehicle’s fuel efficiency, and the current gas price to see exactly how much fuel you’ll need and what it will cost.
Pro tip: Your car’s EPA fuel economy rating is measured under ideal conditions. Real-world MPG is typically 10–20% lower due to driving habits, terrain, weather, and vehicle load. Use your actual observed MPG (trip odometer ÷ gallons filled) for the most accurate cost estimate.
Vehicle A
Vehicle B
How to Use the Fuel Cost Calculator
Enter your trip distance in miles or kilometers, your vehicle’s fuel efficiency (MPG or L/100km), and the current gas price. The calculator instantly shows your total fuel cost, how much gas you’ll need, and your cost per mile. Toggle “Round trip” to automatically double the distance. Use the quick-distance pills for common trip lengths.
Understanding Fuel Efficiency: MPG vs. L/100km
The United States uses miles per gallon (MPG) — higher is better. Most of the world uses liters per 100 kilometers (L/100km) — lower is better. A car rated at 30 MPG is roughly equivalent to 7.84 L/100km. The relationship is inverse, not linear: improving from 15 to 20 MPG saves more fuel than improving from 30 to 35 MPG over the same distance. This is called the MPG illusion, and it means upgrading an inefficient vehicle delivers the biggest savings.
What Affects Your Real Fuel Economy
Several factors cause your actual fuel economy to differ from the EPA rating on your vehicle’s window sticker:
- Speed: Fuel efficiency drops sharply above 50 mph. Every 5 mph over 50 costs roughly $0.15–$0.30 more per gallon.
- Driving style: Aggressive acceleration and hard braking can reduce fuel economy by 15–30% in city driving.
- Tire pressure: Under-inflated tires increase rolling resistance. Every 1 PSI drop costs about 0.2% in fuel efficiency.
- Vehicle load: An extra 100 pounds reduces MPG by about 1–2%.
- Weather: Cold weather (20°F) can reduce fuel economy by 12–20% due to denser air, cold engine oil, and cabin heating.
- Terrain: Mountainous routes use significantly more fuel than flat highways.
How Gas Prices Work
The price you pay at the pump is driven by four main components: crude oil (~55% of the price), refining costs (~15%), distribution and marketing (~10%), and taxes (~20%). Federal excise tax is $0.184 per gallon, and state taxes range from $0.09 (Alaska) to over $0.65 (California). Gas prices vary by region due to proximity to refineries, state tax rates, blend requirements, and local competition.
Tips for Reducing Your Fuel Costs
- Drive at steady speeds and use cruise control on highways.
- Combine errands into a single trip — a warm engine is more efficient.
- Remove roof racks and cargo carriers when not in use (aerodynamic drag).
- Use the recommended fuel grade — premium gas offers no benefit in cars designed for regular.
- Keep up with maintenance: clean air filters, fresh oil, and proper tire pressure.
- Fill up at warehouse clubs or use gas rewards programs for 5–15¢ per gallon savings.
Planning for Long Road Trips
For cross-country drives, fuel cost is often the second-largest expense after lodging. A 2,000-mile trip in a 28 MPG vehicle at $3.50 per gallon costs about $250 in gas. Switching to a 20 MPG SUV for the same trip jumps to $350 — a $100 difference that adds up fast on family vacations. Use the vehicle comparison feature to see exactly how much you’d save by taking the more efficient car, or whether renting a fuel-sipping hybrid would pay for itself on longer journeys.
Looking for related tools? Try our Electricity Cost Calculator to estimate your home energy expenses, or our Percentage Calculator to solve any percent problem instantly. Explore all Everyday Math tools.