An easy way to calculate gas mileage is to remember the odometer reading or to reset the mileage counter when filling up a gas tank. When doing so next time, obtain the mileage accrued between the two gas fill-ups. Then divide the mileage figure by the amount of gas filled the second time to obtain the gas mileage.
How to Improve Gas Mileage?
Carpooling, public transport, or walking/bicycling are the best options for someone looking for the best possible gas mileage, or fuel efficiency. Because they don't involve the use of vehicles, or get the efficient sharing of them! If not viable, here are some pointers to getting the most fuel efficiency:
Drive a fuel-efficient vehicle–Please visit fueleconomy.gov/feg/bestworst.shtml for the fuel efficiency comparison between different vehicles. 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 the same speed at higher speeds.
Tires–Under-inflated tires can lower gas mileage by 0.3% per PSI drop due to wasteful transfer of energy dissipating into the mushiness of the tires when they are underinflated. Rigidity in tires allow for greater frictional interaction between rubber and the road, imparting forward momentum. It is best to consult the driver's manual (also usually available online) or the side markings of the tires to find the optimal PSI range. Also, ensure that wheels are properly aligned.
When allowed by speed limits, 55 MPH (90 km/h) is best–According to studies by the U.S. Department of Energy, the optimal fuel efficient speed is 55 MPH, but may vary depending on vehicles. Obviously, a Lamborghini Aventador will be different than a Toyota Prius. Use cruise control when possible, such as on long, straight, and rural highways (just don't fall asleep at the wheel!). According to the Department of Energy, cruise control can help maintain constant speeds, avoiding unnecessary acceleration and deceleration which is detrimental to fuel efficiency. For most vehicles, as the speed increases from 55 MPH, it is:
3% less efficient at 60 MPH (97 )
8% less efficient at 65 MPH (105 km/h)
17% less efficient at 70 MPH (113 km/h)
23% less efficient at 75 MPH (121 km/h)
28% less efficient at 80 MPH (129 km/h)
Don't be aggressive–Steadiness and consistency wins the race when it comes to fuel efficiency. Aggressive acceleration churns the engine harder, siphoning more oil. Try not to have as heavy a foot as steady acceleration is not only much safer but is more efficient and is kinder to the depreciation of the vehicle. Also, aggressive braking can have a toll on fuel efficiency because drastic drops in speed will only promote drastic increases in speed, on top of faster wear and tear on brakes. Adhering to these principles can improve gas mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic.
Keep vehicles in good shape– It is possible to improve gas mileage by 1-2% simply by using the recommended motor oil. If the driver's manual states 10W-30 as the recommended, do not use 5W-30! Keep the engine properly tuned, ensure the oxygen sensor is in good shape, and solve any failed emissions test right away. Also, check air filters every few months to see if they are clogged; a lot of times, debris from outside gets sucked into them, depriving proper airflow into the engine.
Remove unnecessary weight– This is based on an important physics principle – the heavier the object, the more energy (fuel, in our case) is required to move it. When aiming for best fuel efficiency, driving a smaller, lighter car can be a good start. But anyone can benefit from shedding weight off their current car; try to remove unnecessary items, especially the heavy ones. If there is a huge subwoofer in the back that doesn't work anymore, or bags of concrete in the trunk from last month's patio project, it is probably best to take this weight off the shoulders of the car. Hitching a trailer in the back of a vehicle on everyday commutes to work due to sheer laziness of detaching it from the car is also disastrous to fuel efficiency!
Roll up the windows!–Open windows add extra resistance to moving vehicles. Because highway driving involves such high speeds, a massive burden in the form of drag pushes against the forward momentum of a traveling car, causing the engine to work harder in order to maintain the same speed. Highway driving is usually more fuel efficient when the windows are rolled up to alleviate drag, even with the AC on instead. However, drag, with the scientific term 'wind resistance', doesn't only apply to open windows. If there is a roof rack or bike rack, not only are they adding weight to the vehicle, but the physical presence of their form makes it harder for incoming air to maneuver around a forward moving vehicle!
Air-conditioning–For most drivers, fuel economy suffers during especially hot climates because of partitioning of oil required to power the air-conditioning of the cabin of the vehicles. A vehicle's fuel economy can drop by 25% in hot climates due to AC usage! It can be helpful not to have the AC unnecessarily high, especially when the car is idle; AC systems are more efficient when the car is moving.