Why use this calculator
Tracking your actual fuel efficiency helps you monitor your vehicle's health, identify driving habits that waste fuel, and verify whether your car is performing as expected. Comparing your real-world fuel economy to the manufacturer's rating reveals whether maintenance issues, driving style, or route conditions are affecting your fuel economy. This calculator works with both metric (L/100km) and imperial (MPG) units and converts between them.
How to use it
Select your preferred unit system. Fill up your tank completely, reset your trip odometer, and drive normally until your next fill-up. Record the distance driven and fuel purchased, then enter them here. For the most accurate results, repeat this process over several fill-ups and average the results. Optionally enter the fuel price to see your cost per distance unit.
The formula
Imperial: MPG = Miles Driven / Gallons Used. Metric: L/100km = (Litres Used / km Driven) x 100. Cost Per Distance = (Fuel Price x Fuel Used) / Distance. These formulas give your actual real-world fuel economy.
Worked examples
350 miles driven on 12 gallons of fuel at $3.50/gal
29.17 MPG, 8.07 L/100km, $0.12 cost per mile
560 km driven on 45 litres at $1.80/litre
8.04 L/100km, 29.27 MPG equivalent
When people use it
- Monitoring vehicle health by tracking fuel economy trends over time
- Comparing actual vs. rated fuel efficiency for your vehicle
- Evaluating the impact of driving habits on fuel consumption
- Converting between MPG and L/100km for international vehicle comparisons
Tips
- Track fuel efficiency over multiple fill-ups for a reliable average
- A sudden drop in efficiency can indicate maintenance issues like dirty air filters, low tire pressure, or failing sensors
- Steady highway speeds of 90-105 km/h (55-65 mph) typically give the best fuel economy
- Remove excess weight and roof racks when not in use to improve efficiency
Questions people ask
- What is a good fuel efficiency for a modern car?
- Average fuel economy varies by vehicle type: compact cars 30-40 MPG (6-8 L/100km), midsize sedans 25-35 MPG (7-9 L/100km), SUVs 20-30 MPG (8-12 L/100km), pickup trucks 18-25 MPG (9-13 L/100km), and hybrids 40-60 MPG (4-6 L/100km).
- Why is my actual efficiency worse than the official rating?
- Official tests are conducted under controlled conditions. Real-world factors that reduce efficiency include aggressive driving, high speeds, short trips (engine not fully warmed up), extreme temperatures, hilly terrain, heavy loads, and poor vehicle maintenance.
- What is L/100km and how does it compare to MPG?
- L/100km (litres per 100 kilometres) is the standard fuel consumption metric used outside the US. Lower is better: 6 L/100km is roughly 39 MPG, 8 L/100km is about 29 MPG, and 10 L/100km equals approximately 24 MPG.