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How To Find Out The Fuel Consumption Using Fleet Monitoring

I’m pretty sure you’ve calculated your vehicle’s fuel consumption yourself at least once.

If so, then you have already taken the first step towards “fleet monitoring”. If not, you will do it here.

But, a single, randomly selected fuel economy value isn’t going to help you much. Because you will not be able to answer the following important questions:

  • Can you trust your reading?
  • Is it meaningful and representative?
  • Is it accurate?
  • Is it good or bad compared to other values?

Every time you repeat the exercise, you will find different numbers. Which one do you use for the further procedure? That is not clear.

You need reliable, trustworthy, and meaningful information.

The fleet monitoring method provides you with the required quality of fuel consumption information.

In this and the following articles, I will explain exactly how fleet monitoring is done correctly.

In the end, you can answer the central questions of all consumption determinations because we get to the bottom of the uncertainties.

  • You can use the fleet monitoring method to calculate your fuel consumption values in your use cases.
  • You can use the template I have prepared for you.
  • You can evaluate fleet management IT systems whether they meet the quality standards you expect.

The article “4 Ways To Determine The Correct Fuel Consumption” gives you an overview of all methods of determining consumption. Reading it will help you put fleet monitoring in context with the other, alternative methods.

What is fleet monitoring?

Fleet monitoring is a method of determining the condition of one or more vehicles by collecting vehicle data while driving in real operation. The most interesting aspects to be monitored are the health and fuel consumption of the vehicles.

One might ask: What is the difference between Fleet Management and Fleet Monitoring?

Here is the answer:

Fleet Management looks at the business as a whole. It covers all aspects of managing a fleet of vehicles. You find a very detailed description of all the different functions which can be included in Fleet Management on this website: Wikipedia: fleet management.

Fleet monitoring is an important part of fleet management. It focuses exclusively on the vehicle and the driver. With its help, problems and potential for improvement can be identified. 

When it comes to fuel consumption, we always have to deal with:

  • Measurement errors
  • Systematic influencing factors
  • Random influences

Fleet Monitoring uses a special approach, that I will explain to you in detail. In the end, you know exactly what to look out for.

The Fleet Monitoring method works for passenger cars and trucks. Even so, I will talk about trucks, you can use the same procedure for cars.

Fleet management tools typically include fleet monitoring functions

There is a whole range of software providers out on the market, who offer IT systems for fleet management. These systems provide quick access to the data and advanced functionality, that makes the work easier.

Fleet management software products are offered by vehicle OEMs as well as from suppliers specializing just in this field. Even some component suppliers, like tire companies, are active in this field.

The solutions offered by vehicle OEMs focus typically more on the fleet monitoring aspects of fleet management.

There is a good reason for that.

Vehicle manufacturers have a self-interest in optimizing the fuel consumption of their customers’ vehicles utilizing fleet monitoring.

Providing good advice to the customers is oftentimes a much easier task and more profitable, compared to squeezing out the last fraction of technical efficiency. Fleet monitoring can provide this valuable advice.

For you, it should be welcome. You can use every piece of advice, as long as the fee is less than the saving it realizes.

In this article, I will explain how to do fleet monitoring manually. You don’t need to buy fleet management software to be able to do fleet monitoring. Understanding the manual approach is going to help you to evaluate the IT solutions as well.

How does fleet monitoring help you save fuel?

Why is it important to find out the correct, real fuel consumption?

Because fuel consumption affects two important factors:

  • The operating costs
  • The engine emissions

Both must be lowered so that in the end more money stays in the pocket and the environmental impact is reduced.

That is why reducing fuel consumption is the central issue in the transport industry. It affects vehicle manufacturers as well as fleet owners and drivers.

In order to optimize fuel consumption, it must be continuously monitored.

If you do, you can use this information to spot changes for the better and the worse.

Fleet monitoring not only provides data on fuel consumption but also trends and contextual information.

Knowing this enables you to evaluate the positive and negative changes. By analyzing the related information, you find out what can be influenced and what not.

You can implement changes to the influenceable factors as improvement measures. I will dedicate a special article on this matter.

But you also need to filter out the factors that cannot be influenced. Otherwise, they block the view of the essentials. You will learn in this article how fleet management deals with this task.

If the consumption value is not representative for the entire operation of the vehicle, wrong conclusions are drawn and thus wrong decisions are made.

That would not be good at all. So keep on reading about how to avoid this trap.

How to find out the fuel consumption with fleet monitoring?

Fleet Monitoring uses a large number of fuel consumption values from the real driving of the vehicles to calculate an average fuel consumption. This average value is representative of the conditions under which the fleet is operated. The possible sources of error are identified and taken into account so that the right conclusions can be drawn.

The basic principle of fleet monitoring is to analyze the data from the past and derive conclusions for the future from it.

It takes a certain amount of time to collect the data, so you need patience. As a reward, the predictions for the future are realistic.

Procedure for fleet monitoring

Here is a checklist of the steps you have to take if you do fleet monitoring manually:

  • Fill up the fuel tank,
  • Write down the amount of diesel you put in the tank.
  • Write down the distance driven since the last fuel stop.
  • Calculate and write down the fuel consumption value.
  • During operation: Document as many influencing factors as possible.
  • Calculate the average fuel consumption from as many individual values as possible.
  • Check the scattering of the average consumption value.
  • Analyze the average consumption value and the influencing factors.
  • Compare and conclude. Define improvement measures.
  • Check the improvement measures with further fuel consumption values.

Let’s discuss these steps in detail now.

Collecting the input

Fleet monitoring is based on consumption values from daily use. Unlike all other methods, no special measurements are carried out.

The input values for the calculation of the fuel consumption are the distance traveled and the volume of fuel consumed.

They can be recorded in different ways.

  • Manually when refueling.
  • Through data transmission.
  • Measured and processed directly in the vehicle.

It is important to understand, what to watch out for to avoid measurement errors in all three scenarios.

In the article “Hidden Inaccuracies In Fuel Consumption Measurement” you find detailed information on the errors and inaccuracies, you should be aware of. This subject is so important, that I need to dedicate a special article.

Fuel consumption values as input

In fleet monitoring, the individual fuel consumption values from vehicle operation are used as starting values for calculating the average value.

You can calculate a fuel consumption value for each refueling. I recommend doing this without interruption. If you leave open gaps in your records, it can cause inaccuracy.

The calculation itself is pretty easy:

Divide the diesel volume filled by the distance traveled since the last fuel stop, and then multiply with 100. This gives the fuel consumption in liters per 100 km.

In the article 4 Ways To Calculate Fuel Consumption (incl. calculator) I explain this in detail. There you find also the formula for the people who prefer using miles per gallon instead of l/100 km. Please refer to the headline: “The Relative Fuel Consumption Per Distance.” I strongly recommend reading this article.

Do not use these fuel consumption values to draw conclusions! They are not representative and need further processing.

It’s a shame because it’s so easy to calculate. But don’t worry, it’s not difficult to calculate the average consumption either.

Average consumption as a result

If enough individual values are collected, an average fuel consumption value can be calculated. By doing so, the random influencing factors are averaged out, and only the systematic factors remain visible. This information can now be used for drawing conclusions.

That sounds complicated, but it isn’t! I promise you that you will be able to calculate your values without problems.

Add up your individual consumption values and divide the sum by the number of values.

But wait! There are still some considerations, that you need to take into account before you can trust the result. This matter also deserves a dedicated article. Here you can read how to calculate a trustworthy average fuel consumption value.

At the bottom of the article, you can also request an Excel sheet, which I have prepared for you. It will assist you in doing the calculation.

Now you have the result. But you still have to examine the circumstances under which it came about.

So let’s dive into this.

How does fleet monitoring deal with the influencing factors?

During operation, numerous influencing factors affect fuel consumption and thereby change its value. This is the reason why a different result comes out every time you do this calculation. The difference between the values is called scattering.

In order for the fuel consumption to be meaningful, these influencing factors must be taken into account.

I group the influencing factors into two categories.

  • The random factors
  • The systematic factors

We need to neutralize the random factors so that we can focus on the systematic factors.

What are random influence factors?

A set of dice

Random influencing factors change the fuel consumption, but cannot be influenced consciously. They depend purely on chance.

Since you cannot influence these factors, they are of no interest for fuel consumption improvement.

Their influence on fuel consumption is disturbing. Therefore, we must somehow get rid of them. However, it is important to know and name them.

Here is a list of the main random factors:

  • Ambient temperature
  • Wind force
  • Wind direction
  • Rain
  • Road condition
  • Road curves
  • Driver concentration
  • Traffic density
  • Traffic jam
  • Speed limits
  • Construction sites
  • Slopes

Think if you know any more and write them to me in the comments.

For the classification into random and systematic influences, you have to answer whether you really have no influence on the factor in question.

Factors that can theoretically be influenced, but sometimes not in practice, are nevertheless systematic influences.

Take payload as an example. Often you will not be able to load the vehicle as much as you would like. Nevertheless, you theoretically have an influence on the payload.

Random means: No influence at all.

Take the wind as an example, you really can’t influence it in any way.

This distinction is very important, because the procedure, that I will describe in a moment, only works in the case of really purely random influences.

Chance really needs to be able to do its job.

How does fleet monitoring eliminate the random influencing factors?

In fleet monitoring, we use the chance to rule out chance.

Statistics provide the theory. I will go into detail on this in another article. He is a short summary.

Statistics say, that in a normal distribution, all values are distributed symmetrically around the average value. It can therefore be viewed as representative of all values.

Think of it like this:

If you drive many, many kilometers over many, many years, then on average you will probably climb as many mountains as you descend, you will probably drive in cold temperatures as much as in warm temperatures. And so on and so on ……

Saying this, I talk about probabilities. The area of statistics, therefore, provides the scientific background.

I call the “fleet monitoring” method a “large quantity method”. You need a lot of data for the method to work.

If you really would have an infinite amount of data, the random influencing factors would really be completely averaged out. But that will not be the case, you will always only have a limited number of readings.

This raises the question of whether the number and quality of the input values are sufficient for a precise result.

To be able to judge this, the math gives you the scatter value at hand. The scatter shows you how narrowly or widely the individual values scatter around the average value.

The smaller the scatter, the more you can trust the value.

You will find the calculation of the scatter in the article, which explains the calculation of the average value. It is one of the articles I still have to translate. There will be another article later, that goes into detail about the normal distribution and its most important properties.

If you choose to use my Excel Template, it will calculate the scatter for you.

The key takeaway, how fleet monitoring deals with random influences, is:

The use of a lot of input data leads to an averaging of the random influencing factors and thus to a low scattering of the fuel consumption value.

What are systematic influencing factors?

Trailer with Aeroflaps
The use of air deflectors is a systematic factor. The effect of which can be measured with fleet monitoring.

Systematic influencing factors have a reproducible (repeatable) influence on fuel consumption. In principle, they can be influenced.

Since these factors can be influenced, at least in principle, they offer the potential for deliberately influencing fuel consumption.

That is why they are extremely interesting and exactly what we are actually looking for.

Of course, not everyone can influence everything. There are factors that lie within the vehicle manufacturer’s sphere of influence, while others lie with the driver or entrepreneur.

Here are some examples of systematic influencing factors:

  • Drive train efficiency of the vehicle
  • Payload
  • Curb weight of the vehicle
  • Aerodynamics of the vehicle
  • Rolling resistance of the tires
  • Resistance from the trailer
  • Driving style of the driver
  • Idle time
  • Stand still consumption
  • Fuel consumption of auxiliaries
  • Air conditioning fuel consumption
  • Energy consumption of electrical consumers

Again, I’d love to hear from you about what other factors come into your mind.

How are the systematic influencing factors taken into account?

Whenever a fuel consumption value is calculated, it must be recorded which systematic factors were present during the journey. This record allows identifying the effect of the factors on the fuel consumption.

While we ignore the random consumption factors, we have to be very meticulous about the systematic factors!

You must find a way to correlate the effect of these circumstances with the consumption values.

  • Was it in winter, spring, summer, or fall?
  • What was the average load?
  • What was the tread depth of the tires?
  • What was the tire pressure?
  • and so on ……

The more sorted you document this information, the better you can draw conclusions.

It then goes like this:

  • Evaluate which factors are present in your specific application.
  • Find out how strong their effect is.
  • Investigate whether these factors can be changed.
  • Change the effective, influenceable factors in a positive sense.
  • Check whether the expected positive change actually occurs.

The trick is sorting it all out. You need to spend some time on this task, even if you use fleet management software. You should schedule it!

You can read exactly how this works in the article on optimizing consumption through fleet monitoring, which also follows at a later time.

There will always be systematic factors that can be influenced in principle, but which cannot be changed in your specific case. Likewise, there will also be systematic factors that do not have a strong impact.

Even though they do not provide improvement potential, you still need to take them into account if you compare fuel consumption values with each other.

Here is a list of the systematic factors that you should definitely record in connection with each fuel consumption value:

  • Date (includes season)
  • Vehicle
  • Driver
  • Trailer

The more other influencing factors you document, the more options you have to carry out different evaluations.

How can you document the systematic influencing factors?

The classic method is the logbook. Vehicle, date, fuel quantity, and mileage are included as a minimum.

Another possibility is a spreadsheet in Microsoft Excel, Google Docs, or Mac Numbers. You can create these yourself according to your needs.

If you want, email me, and I’ll send you a Microsoft Excel file.

Here you get a brief impression of what the sheet looks like. You have the possibility to use many columns to document systematic factors in every row of fuel consumption.

You can request the Excel File if you send me your e-mail address using the form below. (In requesting the file, you agree that I can store your E-mail for contacting you in the future. If you don’t want this, please indicate this in the message box below, and I am going to delete your e-mail address after I have sent the file. This service is free of charge, but I accept no liability for the results of the calculations. If you find any errors, you can let me know, and I can make the correction for you)

Who is fleet monitoring suitable for?

Fleet Monitoring requires a large amount of individual fuel consumption values. Therefore, this method is suitable for drivers and entrepreneurs.

You can do fleet monitoring with multiple vehicles or just with a single vehicle. By sorting the data differently, you can carry out different evaluations with the same data and thus examine several optimization approaches at the same time.

With the method, you can examine the effect of measures in your very specific operations. No other method can do this in this quality.

I consider this method indispensable for entrepreneurs, but I also recommend them to all drivers.

Vehicle manufacturers and magazines often do not have the necessary database and the required time. They, therefore, use alternative methods.

You can tell by the fact that they team up with entrepreneurs when they want to take advantage of the realism of this process. An example is the Fehrenkötter test.

What requirements must be met in order to be able to carry out fleet monitoring?

  • A sufficiently large number of fuel consumption values ​​must be available. The more values ​​there are, the more accurate the method is.
  • The operating conditions under which the values ​​are derived must be typical for the transport task.
  • The boundary conditions during the time of determination must contain as many situations as possible that occur in use. (e.g. all seasons)
  • The boundary conditions must be recorded in a table or database together with the individual consumption values.
  • The vehicles must be technically in order.


  • Fleet monitoring can be done by anyone who has enough driving distance on the vehicles
  • A large number of individual values ​​are required so that the random influencing factors are averaged out.
  • The systematic influencing factors should be fully documented.
  • When measuring fuel volume, distance traveled and consumption display, errors can occur that should be observed.
  • Always calculate the average consumption, never just use individual values.
  • Judge the quality of the average fuel consumption by calculating the scattering value.

I wish you every success in using fleet monitoring. Please let me know, how it works for you. Be sure to take a look at the other articles in the fleet monitoring category to really get all the information on the topic.

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