Fuel Cost Calculator: Gas Cost Per Mile & Road Trip Guide

The Fuel Cost Formula

Every trip starts with the same equation:

Total Cost = (Distance ÷ MPG) × Price per Gallon

Where:

• Distance = total miles for your trip
• MPG = your vehicle's fuel efficiency in miles per gallon
• Price per Gallon = current gas price at your destination or along your route

Worked example: a 300-mile road trip in a 28 MPG car at $3.50/gallon:

(300 ÷ 28) × $3.50 = 10.71 gallons × $3.50 = $37.50

That's the base number. Real-world costs run 10–15% higher due to traffic stops, hills, AC load, and speed variation. Our fuel cost calculator handles the math automatically.

Cost Per Mile Formula

For per-mile tracking — useful for commutes, reimbursements, and fleet management — use this simpler formula:

Cost per Mile = Price per Gallon ÷ MPG

At $3.40/gallon with a 28 MPG car: $3.40 ÷ 28 = $0.121 per mile in fuel. Drop your MPG to 20 and that climbs to $0.170 per mile. Improve to 35 MPG and it falls to $0.097 per mile. The difference compounds fast at high annual mileage.

MPG vs L/100km Conversion

If you're working with a European vehicle spec or planning travel in Canada, you'll encounter fuel economy in liters per 100 kilometers (L/100km) rather than miles per gallon. The conversion formulas:

• MPG → L/100km: L/100km = 235.21 ÷ MPG
• L/100km → MPG: MPG = 235.21 ÷ L/100km

Examples: a 28 MPG car = 235.21 ÷ 28 = 8.4 L/100km. A vehicle rated 6.5 L/100km = 235.21 ÷ 6.5 = 36.2 MPG. The constant 235.21 accounts for the unit conversions between miles/kilometers and gallons/liters.

Average Gas Prices (2024–2025)

Accurate fuel cost estimates require current price inputs. Based on EIA (U.S. Energy Information Administration) 2024–2025 data and estimates:

Regional variation is significant. California typically runs $1.00–$1.50/gallon above the national average due to state taxes and reformulated fuel mandates. Gulf Coast states consistently post the lowest prices. Use GasBuddy or the AAA Fuel Gauge Report for real-time prices along your route.

Annual Fuel Cost by MPG (15,000 Miles/Year at $3.40/Gallon)

According to the Federal Highway Administration, the average American drives about 15,000 miles per year. Here's what that costs in fuel across common vehicle efficiency classes:

*EV annual cost calculated at $0.14/kWh (U.S. average residential electricity rate, EIA 2025) and 3.5 miles/kWh efficiency.

AAA's 2025 Your Driving Costs study and EIA consumer expenditure data both peg the average American's annual fuel spending at roughly $2,000–$2,500 per year. That aligns with the 15,000-mile estimate at average prices for vehicles in the 20–28 MPG range.

EV vs Gas Cost Per Mile

The electricity cost advantage for EVs is substantial at home charging rates:

At home-charging rates, EVs cost about $0.03–0.04 per mile compared to $0.12–0.15 per milefor a typical gas car — roughly a 70% reduction. Public DC fast-charging at $0.35–0.50/kWh narrows that gap significantly; at peak rates, an EV on a fast charger can approach the per-mile cost of a gas car. The math still usually favors EVs on road trips, but the advantage shrinks.

Over 15,000 miles/year, the switch from a 28 MPG gas car to an EV charging at home saves approximately $1,215–$1,400 annuallyin fuel alone — before accounting for lower maintenance costs.

How to Improve Fuel Economy

1. Maintain Tire Pressure

Under-inflated tires increase rolling resistance. The U.S. Department of Energy reports that fuel economy improves by about 1% for every 1 PSI increasewhen correcting under-inflation across all four tires. Most cars lose 1–2 PSI per month naturally. Check monthly.

2. Slow Down on the Highway

Aerodynamic drag increases with the square of speed. Per DOE data, fuel economy drops roughly 14% at 70 mph vs. 55 mphand up to 40% at 80 mph. On a 300-mile highway run in a 28 MPG car at $3.40/gallon, dropping from 75 mph to 65 mph saves approximately $3–5 in fuel.

3. Minimize AC in City Driving

AC can reduce fuel efficiency by up to 25% in city driving (EPA estimates). At highway speeds above 45 mph, using AC is actually more efficient than open windows due to aerodynamic drag. In stop-and-go traffic, crack the windows and use the fan instead.

4. Eliminate Unnecessary Idling

Idling gets 0 MPG. A car idling for 10 minutes burns roughly 0.2–0.5 gallons of gas. DOE estimates that idling costs the average driver $100–200/year. Modern engines warm up faster driving slowly than sitting still.

5. Combine Errands and Optimize Routes

Cold engines are 10–15% less efficient for the first several miles. Combining three separate cold-start errands into one trip can reduce that overhead to a single warm-up. Route optimization apps (Google Maps, Waze) also cut unnecessary miles.

Road Trip Fuel Budget Planning

Planning a long road trip? Here's how to build an accurate fuel budget using the formula, then stress-test it.

NYC to Los Angeles Example

The standard route from New York City to Los Angeles via I-40 is approximately 2,800 miles. In a 28 MPG midsize sedan at $3.40/gallon:

(2,800 ÷ 28) × $3.40 = 100 gallons × $3.40 = $340 in fuel

Add a 12% real-world buffer (traffic through cities, elevation changes, AC load): $340 × 1.12 = ~$381 total. That's the fuel budget for one direction. Round trip: approximately $760. Plan roughly 7–8 fill-ups at an average of 13–14 gallons per stop.

How Fuel Fits Into Total Trip Cost

According to FHWA and AAA consumer data, fuel typically accounts for 20–30% of total domestic road trip spending(the rest going to lodging, food, and activities). On a $1,500 total trip budget, that's roughly $300–$450 in fuel — consistent with the math above for a multi-day drive.

Frequently Asked Questions

How do you calculate fuel cost for a road trip?

Use this formula: Total Cost = (Distance ÷ MPG) × Price per Gallon. For a 300-mile road trip in a car that gets 28 MPG at $3.50/gallon, that's (300 ÷ 28) × $3.50 = $37.50. Add a 10–15% buffer for real-world conditions like traffic, hills, and AC load.

How do I calculate cost per mile for gas?

Cost per Mile = Price per Gallon ÷ MPG. At $3.40/gallon with a 28 MPG car, you pay $3.40 ÷ 28 = $0.121 per milein fuel. A more fuel-efficient 35 MPG car drops that to $0.097 per mile — saving nearly $365 per year at 15,000 annual miles.

How much does it cost to drive 1 mile?

For a gas car averaging 28 MPG at $3.40/gallon, driving one mile costs about $0.12 in fuel. Hybrids at 45 MPG cost around $0.076 per mile. Electric vehicles cost roughly $0.03–0.04 per mileat home charging rates of $0.14/kWh — making them by far the cheapest option per mile on fuel.

Is it cheaper to drive an EV or a gas car?

EVs are significantly cheaper per mile on fuel. At $0.14/kWh electricity and 3.5 miles/kWh efficiency, an EV costs about $0.040 per mile. A gas car at 28 MPG and $3.40/gallon costs $0.121 per mile— three times more. Over 15,000 miles/year, that's roughly $1,215 in annual fuel savings. Public fast-charging narrows the gap but home charging keeps EVs well ahead on operating cost.

How does driving speed affect fuel costs?

Significantly. According to the U.S. Department of Energy, fuel economy falls roughly 14% at 70 mph compared to 55 mph due to aerodynamic drag. At 80 mph, the penalty reaches 30–40%. On a 300-mile highway trip in a 28 MPG car at $3.40/gallon, driving 70 mph instead of 55 mph adds approximately $2.75 in fuel cost. Over a year of highway driving, slowing down can save $100–200.