Cost Calculator AI
Cars & VehiclesOdometer Method

Gas Mileage Calculator (MPG)

Calculate your car’s actual real-world miles per gallon (MPG) using trip odometer readings and gallons pumped at fill-up, with instant L/100km and km/L conversions.

Calculation Results

Standard Odometer Gas Mileage Formula

Actual MPG = (Ending Odometer − Starting Odometer) / Gallons Pumped at Fill-Up
  • Trip Meter Method: Trip Miles / Gallons Pumped.
  • Metric L/100km Equivalent = 235.215 / US MPG.
  • Km per Liter Equivalent = US MPG × 0.425144.

Step-by-Step Worked Example

Scenario: Driving 345 miles on a road trip and pumping 11.5 gallons to full

Calculation Steps:

  1. Calculated MPG = 345 miles / 11.5 gallons = 30.0 MPG
  2. Liters per 100 km = 235.215 / 30.0 = 7.84 L/100km
  3. Cost per Mile = $3.50 / 30.0 MPG = $0.117 / mile
Result: Your vehicle achieved 30.0 MPG (7.84 L/100km), costing 11.7¢ per mile in fuel.

How to Use This Calculator

  1. 1Fill your gas tank completely and reset your trip odometer to zero.
  2. 2At your next fill-up, note the trip miles and the exact gallons pumped from the receipt.
  3. 3Input the values into the calculator to see your precise real-world fuel economy.

Assumptions & Limitations

  • Requires filling the tank to the first automatic shut-off click at both start and end.

Frequently Asked Questions

Why is my actual gas mileage lower than the EPA sticker?

EPA ratings are tested in controlled laboratory settings. Real-world driving involves winter cold temperatures, air conditioning, roof racks, aggressive acceleration, short trips, and ethanol-blended fuels, which typically reduce MPG by 10% to 15%.

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