Understanding Gas Mileage and Fuel Efficiency
Gas mileage, also known as fuel efficiency, measures how far your vehicle can travel per unit of fuel consumed. It's typically expressed as Miles Per Gallon (MPG) in the US or Liters per 100 kilometers (L/100km) in metric countries.
Understanding your vehicle's gas mileage helps you budget for fuel costs, compare vehicle efficiency, and make informed decisions about driving habits and vehicle purchases.
Basic Gas Mileage Formula
How to Improve Gas Mileage
Drive Efficiently: Carpooling, public transport, or walking/bicycling are the best options for someone looking for the best possible gas mileage, or fuel efficiency.
- Drive a fuel-efficient vehicle – Overall, 4-wheel drive vehicles tend to be less fuel efficient than FWD or RWD. By powering all four wheels, the engine works harder to move a car at higher speeds.
- Tires – Under-inflated tires can lower gas mileage by 0.3% per PSI drop due to wasteful energy transfer. Ensure proper tire pressure and wheel alignment.
- Optimal Speed: 55 MPH (90 km/h) – According to studies by the U.S. Department of Energy, the optimal speed for fuel efficiency is 55 MPH. Relative to 55 MPH, vehicles are on average:
| Speed |
MPH |
km/h |
Efficiency Loss |
Impact |
| Optimal | 55 | 90 | 0% | Best efficiency |
| Highway | 60 | 97 | 3% | Slight decrease |
| Fast Highway | 65 | 105 | 8% | Noticeable loss |
| Very Fast | 70 | 113 | 17% | Significant loss |
| Excessive | 75 | 121 | 23% | Major loss |
| Dangerous | 80 | 129 | 28% | Severe loss |
- Don't be aggressive – Aggressive acceleration and braking can reduce gas mileage by 15-30% at highway speeds and 10-40% in stop-and-go traffic.
- Keep vehicles in good shape – Proper maintenance can improve gas mileage by 1-2%. Use recommended motor oil, keep engine tuned, replace air filters, and fix emissions issues promptly.
- Remove unnecessary weight – Every 100 pounds of extra weight can reduce efficiency by 1-2%. Remove heavy items not being used regularly.
- Roll up the windows – Open windows create drag at highway speeds. Use AC instead of open windows during highway driving for better efficiency.
- Air-conditioning – AC can reduce fuel economy by up to 25% in hot climates. Use it efficiently and avoid unnecessarily high settings.
- Avoid unnecessary idling – An idle vehicle gets 0 MPG. Turn off the engine for stops longer than 30 seconds.
Fuel Efficiency Comparison by Vehicle Type
| Vehicle Type |
Typical MPG |
L/100km |
Efficiency Rating |
Best For |
| Large SUV/Truck | 15-18 | 13-16 | Poor | Heavy hauling |
| Mid-size SUV | 20-25 | 9-12 | Below Average | Family transport |
| Sedan (Full-size) | 25-30 | 8-9 | Average | Comfort + efficiency |
| Compact Car | 30-35 | 7-8 | Good | City driving |
| Subcompact | 35-40 | 6-7 | Very Good | Economy transport |
| Hybrid | 40-50 | 5-6 | Excellent | Maximum efficiency |
| Plug-in Hybrid | 50-100 | 2-5 | Outstanding | Short electric range |
Factors Affecting Gas Mileage
Driving Conditions: City driving typically reduces fuel efficiency by 20-40% compared to highway driving due to frequent stops, starts, and lower average speeds.
Weather Impact: Cold weather can reduce gas mileage by 10-40% for short trips, as engines take longer to reach optimal efficiency. Hot weather increases AC usage, reducing efficiency.
Vehicle Condition: Poor maintenance, worn tires, dirty air filters, and engine problems can significantly reduce fuel efficiency. Regular maintenance is crucial.
Environmental Benefits
Improving gas mileage not only saves money but also reduces environmental impact. Better fuel efficiency means:
- Reduced CO2 emissions and air pollution
- Lower dependence on fossil fuels
- Conservation of natural resources
- Contribution to cleaner air quality
Tip: Track your gas mileage regularly using this calculator to identify trends and the effectiveness of efficiency improvements.