Mileage Calculator Guide: Calculate Fuel Cost, MPG & Trip Expenses

Fuel cost for any trip = (distance ÷ fuel economy) × fuel price

Example: 350-mile road trip, car gets 28 MPG, gas costs $3.50/gallon • Gallons needed: 350 ÷ 28 = 12.5 gallons • Cost: 12.5 × $3.50 = $43.75

For metric units: • Fuel cost = (distance in km ÷ 100) × fuel consumption (L/100km) × price per liter • Example: 500 km trip, 8L/100km vehicle, $1.60/L: (500 ÷ 100) × 8 × 1.60 = $64.00

For longer road trips, plan your fuel stops: calculate gallons at each stop based on available range (tank capacity × MPG), and check prices along the route using GasBuddy or Google Maps.

• Fuel cost = (miles ÷ MPG) × price per gallon
• Gallons needed = miles ÷ MPG
• Range on a full tank = tank capacity (gallons) × MPG
• GasBuddy and Google Maps show real-time gas prices along routes

The most accurate MPG measurement comes from fill-up data:

Method: 1. Fill the tank completely and note the odometer reading (start_miles) 2. Drive normally until the next fill-up 3. Fill completely again and record: gallons added and new odometer (end_miles) 4. MPG = (end_miles − start_miles) ÷ gallons added

Example: • Odometer at fill 1: 45,210 miles • Odometer at fill 2: 45,517 miles • Gallons added: 10.3 • MPG = (45,517 − 45,210) ÷ 10.3 = 307 ÷ 10.3 = 29.8 MPG

Track several fill-ups for an average — MPG varies with driving conditions, temperature, and fuel quality.

• Fill completely, record odometer, fill completely again — divide miles by gallons
• MPG = (ending odometer − starting odometer) ÷ gallons added
• Track 3–5 fill-ups and average for reliable baseline
• Cold weather, AC, and aggressive driving reduce MPG by 10–25%

The IRS sets standard mileage rates annually for business driving deductions:

2024 IRS mileage rates: • Business use: 67 cents per mile • Medical or moving (certain active-duty military): 21 cents per mile • Charitable: 14 cents per mile

For employee reimbursement, many companies use the IRS rate as the standard: drive 150 miles for business, receive 150 × $0.67 = $100.50.

Self-employed and business owners can deduct actual vehicle expenses OR the standard mileage rate (but not both). The standard mileage method is simpler; the actual expense method (gas + maintenance + depreciation + insurance) may be higher for fuel-inefficient vehicles.

Mileage log requirements: the IRS requires documentation of date, destination, business purpose, and miles for every business trip.

• 2024 IRS business mileage rate: 67 cents per mile
• Medical/military moving: 21 cents/mile | Charitable: 14 cents/mile
• Standard mileage vs. actual expense: calculate both to determine which is higher
• IRS requires: date, destination, purpose, and miles for every trip in your log

Understanding what hurts MPG helps you optimize:

Speed: fuel economy peaks at 45–55 mph for most vehicles. At 70 mph, fuel economy drops approximately 15–20% compared to 55 mph. At 80 mph: 25–30% penalty.

Acceleration and braking: aggressive acceleration and hard braking (jackrabbit driving) reduces fuel economy by 15–30% in city conditions. Smooth driving saves fuel.

Air conditioning: AC decreases fuel economy by 5–25% depending on conditions. At highway speeds, AC vs. open windows: approximately equal. In stop-and-go, windows are slightly better.

Tire pressure: under-inflated tires reduce MPG by ~0.2% per PSI below optimal. Keep tires at manufacturer-recommended pressure (on the door jamb, not the tire sidewall).

Cargo and weight: every extra 100 lbs reduces fuel economy by about 1–2%. Remove unnecessary cargo from your trunk.

• Speed: optimal fuel economy at 45–55 mph; 70 mph = 15–20% MPG penalty
• Aggressive driving: 15–30% fuel economy reduction vs. smooth driving
• AC: 5–25% MPG reduction; minimal difference vs. windows at highway speeds
• Tires: under-inflation reduces MPG; check pressure monthly

Fuel is typically 20–25% of total vehicle operating cost. The full picture:

IRS's 67 cents/mile all-in estimate accounts for: • Fuel: approximately 12–18 cents/mile (varies by MPG and gas price) • Depreciation: typically 15–20 cents/mile for an average vehicle • Insurance: approximately 8–12 cents/mile • Maintenance and tires: 5–8 cents/mile • Registration and taxes: 2–3 cents/mile

For comparison: owning and operating an average car in 2024 costs approximately $900–$1,200/month when all costs are included (for 15,000 miles/year). A $3.50/gallon price for a 28-MPG car is only ~$150/month in fuel alone.

• Fuel = only 20–25% of total vehicle cost; depreciation is often the largest cost
• IRS 67¢/mile captures all-in operating costs for average vehicle
• Depreciation: average car loses $3,000–$5,000 in value per year
• Total ownership: $900–$1,200/month for average US vehicle (2024)

For electric vehicles, the equivalent of MPG is MPGe (miles per gallon equivalent):

MPGe = miles per 33.7 kWh (one gallon of gasoline contains ~33.7 kWh of energy)

Cost per mile for EV: (kWh per mile) × (electricity price per kWh) Example: EV uses 0.3 kWh/mile, electricity costs $0.15/kWh • Cost per mile: 0.3 × $0.15 = $0.045 (4.5 cents/mile vs. ~12–16 cents/mile for gasoline)

EV range calculation: (battery capacity in kWh) × efficiency (miles/kWh) Example: 75 kWh battery, 3.5 miles/kWh → range ≈ 262 miles

EV efficiency drops significantly in cold weather (20–40% range reduction below freezing) and at highway speeds above 65 mph.