Gas Cost Calculator — Estimate Fuel Cost for Any Road Trip

Trip Fuel Cost Calculator

Average Fuel Efficiency by Vehicle Type

Not sure about your vehicle's fuel efficiency? Use these averages as a starting point:

Values are estimates for combined city/highway driving. Check your vehicle's specifications or use the EPA's fueleconomy.gov for accurate data.

How It Works

This calculator uses a simple formula to estimate your trip fuel cost:

For imperial units (US):

• Distance in miles
• Fuel efficiency in miles per gallon (MPG)
• Gas price in dollars per gallon

For metric units:

• Distance in kilometers
• Fuel efficiency in liters per 100 km (L/100km)
• Gas price in your currency per liter

CO₂ emissions are estimated using average values: 8.89 kg CO₂ per gallon of gasoline (or 2.35 kg per liter).

Tips to Save on Gas

• Maintain proper tire pressure — Underinflated tires reduce fuel efficiency by up to 3%
• Drive smoothly — Aggressive acceleration and braking can lower MPG by 15-30%
• Use cruise control — Maintains steady speed on highways, improving efficiency
• Remove excess weight — Every 100 lbs reduces fuel economy by about 1%
• Plan your route — Combine errands and avoid peak traffic when possible
• Check gas prices — Apps like GasBuddy can help find cheaper stations nearby

Worked Examples

Example 1: Weekend Road Trip

You're driving 350 miles round trip. Your car gets 28 MPG, and gas is $3.40/gallon.

Example 2: Cross-Country Drive

A 2,800-mile trip in an SUV averaging 22 MPG, with gas at $3.65/gallon.

Example 3: Metric — City Commute

Daily commute of 40 km round trip in a car rated at 7.5 L/100km, with fuel at €1.75/liter.

Cost Comparison: How Vehicle Type Changes Trip Cost

Same 500-mile trip at $3.50/gallon — the vehicle you drive makes a big difference:

A pickup truck costs nearly 3× more in fuel than a hybrid for the same trip.

Frequently Asked Questions

How do I calculate gas cost for a road trip?

Divide your trip distance by your car's MPG to find gallons needed, then multiply by the gas price. Formula: Cost = (Distance ÷ MPG) × Price per gallon. For example, 300 miles at 25 MPG with $3.50 gas = 12 gallons × $3.50 = $42.00.

How much gas will I need for a 500-mile trip?

It depends on your vehicle's fuel efficiency. At 25 MPG: 20 gallons. At 30 MPG: 16.7 gallons. At 35 MPG: 14.3 gallons. Multiply by your local gas price for the dollar amount.

How do I find my car's MPG?

Check your owner's manual, the sticker inside your driver's door, or look up your vehicle on fueleconomy.gov. For real-world accuracy, divide miles driven since your last fill-up by gallons pumped.

What is the average cost per mile to drive?

Fuel cost per mile depends on gas price and MPG. At $3.50/gallon and 25 MPG, it's $0.14/mile. Total driving cost including insurance, maintenance, and depreciation typically ranges from $0.50 to $0.80/mile.

Why is my actual fuel cost different from the estimate?

Real-world fuel efficiency varies based on driving conditions (city vs. highway), traffic, weather, terrain, tire pressure, A/C use, speed, and driving habits. EPA ratings reflect controlled test conditions, not everyday driving.

Does driving speed affect gas cost?

Yes. Fuel efficiency drops noticeably above 50 mph due to increased aerodynamic drag. Each 5 mph over 50 is roughly equivalent to paying an extra $0.15–$0.30 per gallon. Cruising at 60–65 mph is typically the most fuel-efficient highway speed.

How do I convert MPG to L/100km?

Divide 235.215 by the MPG value. For example, 30 MPG = 235.215 ÷ 30 ≈ 7.84 L/100km. Higher MPG means lower L/100km (better efficiency).

How are CO₂ emissions calculated from fuel use?

Burning one gallon of gasoline produces approximately 8.89 kg (19.6 lbs) of CO₂. One liter produces about 2.35 kg. These are fixed chemical properties of gasoline combustion — the only variable is how much fuel you burn.

Is this calculator accurate for diesel vehicles?

The fuel cost math is the same. Enter your diesel MPG and diesel price per gallon for an accurate cost estimate. The CO₂ figure will be slightly underestimated since diesel produces about 10.18 kg CO₂ per gallon vs. 8.89 for gasoline.

How much does a round trip cost in gas?

Exactly double the one-way cost. A 200-mile one-way trip at 25 MPG with $3.50 gas costs $28, so the round trip costs $56. Check the "Round trip" box in the calculator above for an instant estimate.

How can I reduce gas costs on a long trip?

Maintain steady speed with cruise control, keep tires properly inflated, avoid idling, remove roof racks when not in use, travel during off-peak hours to avoid stop-and-go traffic, and fill up at cheaper stations along your route.

Does this calculator store my data?

No. All calculations run entirely in your browser using JavaScript. No data is sent to any server, and nothing is stored or tracked.

Learn More

For a deeper dive into fuel economy, how MPG and L/100km work, and what factors affect your real-world gas mileage, read our guide: How to Calculate Gas Cost for a Road Trip.

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