How to calculate your car's mileage correctly?

There are a lot of factors that go into judging a car’s performance. The most common talking points are the ones that focus on a car’s power and torque figures, or how much the car in question weighs, or even how aerodynamic it is. But arguably one of the most important things to consider about a car is how efficiently it consumes fuel.

A car’s fuel consumption is a crucial thing to understand because it will not only give you a realistic estimate of how many kilometres it will cover on a single tank of fuel (or, if it’s an electric vehicle, how many kilometres it will cover until you have to recharge the battery), but also how it will impact your monthly and annual budget. It's important to know how to calculate mileage as it gives you a good idea of the amount of kilometres your car can cover for every litre of fuel consumed, and you can estimate how much your car will travel in a month, then understanding how much money you will need to set aside for fuel will become easy. It’s also important to know your car’s accurate mileage when it’s time to sell your car. While it’s not a guarantee, if your car is efficient with its fuel consumption, you’re likely to get a better resale value. 

Thanks to ever-escalating fuel prices, it’s not a stretch to admit that our country is dependent on fuel efficient vehicles. Given all that, how do you calculate your car’s mileage accurately? What can you do to improve your car’s mileage? And does your driving technique affect your car’s mileage? In our guide on how to calculate your car’s efficiency, we will answer all those questions, and more.

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What is car mileage?

Car mileage is a way to measure a car’s fuel efficiency. Put simply, for cars with internal combustion engines, it tells you how many kilometres your car will run on a single litre of fuel. For electric vehicles, its efficiency is gauged by finding out how many kilometres the vehicle will run before the battery is fully drained.

The amount of factors that directly affect a car’s efficiency are too many to list. Broadly speaking though, it boils down to the size of the engine, whether petrol or diesel is used, the overall weight of the car, and what components the car’s equipped with that either help boost efficiency (like cylinder deactivation tech) or reduce it.

As for how mileage is expressed, there are a few commonly used units:

1) Kilometres per litre (kmpl): This is the most commonly used unit to express fuel efficiency in India. It indicates how many kilometres a car can travel in one litre of fuel.

2) Litres per 100 kilometres (l/100 km): A less common way to refer to fuel efficiency in India, but it has considerable use abroad. It’s also why some cars give you the option of displaying its fuel efficiency in l/100 km in India.

3) Miles per gallon (mpg): This unit of measurement is primarily used in the United States and some other countries. Since they are one of the few countries in the world to use the imperial system of measurement (India uses the metric system), they measure in miles per gallon. It represents the same concept, except for conveying how many miles a car can travel on a gallon of fuel.

ARAI-rated figures vs. real-world figures

A point to note here is that almost every car sold in India comes with an Automotive Research Association of India (ARAI)-rated fuel efficiency figure. ARAI is, as the name suggests, a co-operative governmental body that focuses on automotive research & development and evaluating automotive industry products and equipment.

So, as an example, while it may label a car’s efficiency to be 15 kmpl, the likelihood is that the real efficiency owners get undercuts that figure by a fair margin. The reasons for the discrepancy can easily be explained.
1) The ARAI test is done using a chassis dynamometer which aims to simulate the Indian Driving Cycle (IDC) to test the cars in conditions as close to the real world as possible. The test tries to achieve this by taking into consideration several forces that act upon a car in actual conditions (like inertia). However, the simulation is not a close match for the actual driving conditions. That’s why the fuel efficiency figures for a car tested on a dynamometer don’t entirely tally with real-world figures.

2) The ARAI test has a duration of a mere 19 minutes for a distance of 10 kilometres with the simulated city and highway road conditions on a dynamometer at an average speed of around 31 kmph. The speeds do not exceed 90 kmph. Naturally, these are hardly representative of real-world driving conditions, and is another reason why ARAI fuel efficiency figures differ from real-world figures.

All the same, car manufacturers continue to use ARAI-rated figures because they bring a certain level of uniformity to all the cars on sale, and hence it becomes easier to compare and evaluate choices.

How to calculate your car’s mileage

One of the most reliable ways to calculate your car’s real-world efficiency involves a straightforward process that’s easy to action.

1) Fill up your car’s fuel tank to the brim. Ensure that the fuel gauge reads ‘Full’ or ‘F’.

2) Reset your car’s trip metre. This will allow you to track the distance travelled during this fuel cycle.

3) Continue to drive how you normally would. To that effect, if city traffic runs, highway runs, and even grocery runs figure in your regular driving cycle, they should all be part of the calculation.

4) Once the car’s fuel gauge is nearing empty, refuel your car again. Pay close attention to the amount of fuel that has gone in this time around.

5) You can now get the mileage by dividing the total distance travelled by the amount of fuel consumed.

As an example: if you drove for 450 kilometres and consumed 30 litres of fuel, your mileage will be 450 kilometres divided by 30 litres. That equals 15 kmpl.

Formula to calculate mileage

The formula to calculate mileage is as follows:
 

Total distance travelled (km) / amount of fuel consumed (litres) = Mileage (kmpl)

Tips for accurate mileage calculation

While conducting fuel efficiency runs, there are a few things to keep in mind, namely:
1) Make sure you have consistent driving conditions. Avoid exceptionally heavy traffic conditions or even extreme weather conditions for accurate results.

2) Be sure to fill the fuel tank completely to get precise measurements.

3) Ensuring your car is well-maintained and serviced is also a key factor. This is a practice that should be adhered to even when you aren’t conducting fuel economy tests.

4) Your tyre pressures should be at the recommended psi levels to ensure an accurate fuel economy readout. If you are not sure what pressure is optimal, it’s best to stick to the manufacturer-recommended pressures.

5) Jerky acceleration and braking inputs should be avoided as they cause unnecessary stress on the engine, which could lead to exaggerated fuel economy readouts.

Why is it important to calculate your car’s mileage 

Monitoring your car’s fuel efficiency can be beneficial in a lot of ways, and there are lots of good reasons behind regularly checking your car’s fuel consumption:

1) It will get you into the habit of identifying your car’s fuel consumption over a longer period of time. This will be useful to spot an issue early if the fuel consumption drops unexpectedly. It could mean that there’s something wrong with your car’s engine, and a quick visit to your car technician will be able to spot the problem and help rectify it.

2) Monitoring your car’s average is useful when evaluating the impact of different fuel types on your car’s performance.

3) If you notice drastic variations in your fuel consumption and there’s nothing wrong with your engine, then it could mean that your driving habits need optimising. 

Factors affecting car mileage

There are plenty of factors that affect the kind of mileage a car returns. These factors include:

1) Weight of the car: Heavier cars (like SUVs) tend to have lower mileage.

2) Engine size: Larger engines tend to consume more fuel.

3) Aerodynamics: A car’s shape affects its fuel economy. As an example, a car that’s designed with plenty of sharp cuts and right angles won’t allow an uninterrupted airflow, which causes drag, which leads to a higher fuel consumption.

4) Tyre condition: If a car’s tyres are underinflated, there’s a strong chance that fuel consumption will increase.

5) Driving conditions: Traffic, weather, and road conditions impact mileage. As an example, the heavier the traffic, the more start-stop conditions there will be, which leads to the engine being under more stress, and that eventually leads to a higher fuel consumption.

6) Fuel quality: Using higher quality fuel can improve mileage.

7) Car maintenance: A regular car service schedule can optimise engine performance and increase fuel efficiency.

Impact of driving habits on mileage

It’s hard to underestimate the impact your driving habits have on fuel economy. Progressive and smooth accelerator inputs can greatly improve fuel efficiency, as can cruising at constant speeds on highways and wherever possible. A big way to influence fuel economy is also to anticipate what the traffic ahead is about to do. This will help plan your braking, leading to smoother accelerator and brake inputs.

It’s also a good idea to consider switching the air conditioning off when it’s not required in a car. It increases the load on the engine, and in turn saps fuel. And finally, a good practice is to switch the engine off at signals when you know the car will be stopped for extended periods. 

Tips for improving mileage through driving habits

There are quite a few things you can do to influence your car’s fuel consumption. Adopting these practices can help significantly boost your car’s mileage:

1) Smooth acceleration and braking: Gentle acceleration and braking reduce fuel wastage. Even if you own a car with the best reported mileage figure, jerky accelerator and brake inputs can drastically reduce your mileage.

2) Maintaining a steady speed: Cruise at a constant speed whenever possible to optimise fuel efficiency.

3) Avoid idling: Turn off the engine when stopped for extended periods.

4) Tyre pressure: Ensure proper tyre inflation. Underinflated tyres increase fuel consumption.

5) Gear shifts: Shift gears smoothly and avoid lugging the engine. Whenever possible, try shifting up a gear to keep the engine revs at a low level.

6) Air conditioning: Use it judiciously as it increases engine load.

7) Car load: Reduce unnecessary weight in the car. The heavier your car is, the more fuel it will consume.

8) Driving conditions: Avoid heavy traffic and extreme weather conditions.

9) Eco driving mode: Some cars come with driving modes. One of them is typically an ‘Eco’ or ‘Green’ mode. Regardless of what it’s named, it dulls throttle responses and helps boost efficiency.

10) Regular maintenance: Keep your car well-maintained for optimal performance.

Conclusion

Ensuring you know exactly how much fuel your car consumes over a defined period is important for a number of reasons. The better your car’s mileage is, the less you will have to pay for fuel, and it’s also directly proportional to how valuable your car will be when it comes time to sell it.

In a country as sensitive to prices as ours, it’s important to ensure that your car is as efficient as possible. While it’s true that there are a few factors influencing a car’s fuel economy that are out of our control (like its shape, and its overall weight), there are quite a few things we can do that are within our control to help improve a car’s mileage.

FAQs

Q. What is the formula to calculate mileage?

The formula to calculate a car’s mileage is: Total distance travelled (km) / amount of fuel consumed (litres) = Mileage (kmpl)

Q. How do I calculate mileage for a long trip?

The easiest way to calculate mileage for a long trip is to find out the total kilometres covered, and then dividing that number by the amount of litres of fuel your car has consumed in that period. 

Q. Can driving at night affect mileage?

It can. If the roads are poorly lit and your car’s lights aren’t effective, then you might be prone to jerky accelerator and brake inputs, which will lead to higher fuel consumption.

Q. How often should I track my mileage?

Tracking your mileage at least once a month is recommended.

Q. Is mileage affected by weather conditions?

Yes. Heavy rain or snowfall can create an additional load on the engine, which leads to reduced fuel efficiency.

Q. What should I do if my mileage suddenly drops?

Head to your nearest trusted mechanic to get a diagnosis at the earliest.

Q. Are there any mileage-enhancing gadgets worth investing in?

Fuels with additives are worth considering for improved fuel economy.

Q. How do I account for city vs. highway driving in mileage calculations?

Typically, a driving cycle with city and highway conditions involved leads to a more accurate representation of fuel economy.

Q. Does the weight of passengers and cargo affect mileage?

Yes. The more load there is on the car’s engine, the poorer the mileage will be.

Q. How does altitude impact mileage?

Higher altitudes negatively impact a car’s mileage. The higher the altitude, the thinner the air. Thinner air means the engine isn’t able to burn fuel as efficiently, which leads to poor fuel economy.