What is a car trip computer?

Almost all modern cars have trip computers, but what are these systems, and how do they work?

The first electronic trip computer came along in 1978 and was fitted to the Cadillac Seville. Mechanical systems had existed prior to that, but the Seville’s ability to calculate its own fuel economy and allow the driver to input the number of miles to their destination was a novel idea.

Car trip computers have evolved and become more sophisticated since then (especially where electric cars are concerned), but the principle behind them has remained unchanged. Here, we detail what a trip computer is, how it works, and what sort of information you can reasonably expect to be fed by one.

What do trip computers do?

The trip computer on a Mercedes C63 showing (from L to R, top to bottom) the distance traveled, the time taken, average fuel consumption and average speed

As the old adage goes, a trip computer does what it says on the tin: it computes data linked to a trip.

There are a five key areas that a trip computer provides information on:

  • Time
  • Distance
  • Speed
  • Fuel consumption
  • Range

Each of these four areas has layers of information to it, and while precisely what a trip computer shows will vary from car to car, you can reasonably expect the following:


Trip computers will tell you how long you have been traveling since you started your journey. If linked to the sat-nav, they can also tell you how long you have to go until you reach your destination.


As you can imagine, this will tell you how the car has traveled.


This will provide you with the average speed the car has traveled.

Fuel consumption

This will generally provide two readings: your car’s average fuel consumption, and instant fuel consumption – IE how what mpg the car is doing from one moment to the next, allowing you to see how different conditions (EG hills, speed, how aggressive you are with the accelerator) affect fuel consumption.


This will tell you how far you can go before your fuel tank is empty. While generally speaking the range figure will decrease as your journey goes on and you deplete the fuel tank, the range figure may actually increase if you start a journey in town and then head out on the open road where efficiency is better, as the calculations will change based on your driving as the trip goes on.

Trip computers: Trip A and Trip B

Many trip computers provide information for three ‘trips’: Trip A, Trip B, and since reset.

This allows all the information detailed above to be measured separately and in parallel across three time periods. You can reset each trip individually, or reset all at once.

As an example, you may want to use Trip A to determine how far, how fast and how efficiently the car goes on each tank of fuel, resetting Trip A each time you fill up the tank.

You may also, however, want to see if a new route to work takes less time, provides better fuel economy or is faster than your usual route. You could therefore reset Trip B to determine this, while leaving trip A to keep ticking along in the background until you next need to fill up with fuel.

As for the ‘since reset’ information, many people never touch this, meaning it may show how far, fast and efficiently the car has traveled since it left the factory (or possibly since its battery was last removed).

Do also note that if you make a series of short journeys (EG pick the kids up from school, pop into the supermarket, head over to football practice) those journeys will often be treated as a single trip by car, which will typically reset itself to a new ‘trip’ after the car has been switched off for four hours or so.

Electric car trip computers

The Audi e-tron GT’s display, showing the remaining range

Perhaps the biggest change to come to the world of trip computers has been brought about by the advent of electric cars.

An EV’s trip computer will typically show you all the information covered above, as well as the electric equivalent of fuel economy: instead of miles per gallon, you will be shown miles per kiloWatt hour (EG if you have a 100kWh battery and the car does 3 miles per kWh, you will get 300 miles from a charge – see here for more information.)

In addition to this, many EVs will synchronize their battery ranges with the sat-nav, calculating how far you can go on a charge, and where you will need to stop to recharge if you are undertaking a long journey.

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