How to calculate the GS from IAS

Firstly, is the speed shown in the cockpit shown as ground speed or air speed. If it is in air speed how can I estimate the speed it should be in Ground speed?

If you look on top of the mini map you should see something that say GS and right next to it a number . If you cant find this you can change the instrument dock on the bottom and select ground speed


The one in red is where the airspeed is mentioned. The one in yellow next to the ‘GS’ is where the ground speed is mentioned.


The speed displayed on your airspeed indicator in the cockpit is, of course, airspeed. Ground speed is found by adding or subtracting (depending where the wind is coming from) external wind speeds to your airspeed to determine how fast you’re actually moving in relation to the ground. For example, if you have a 15 knot headwind and your airspeed indicates 75 knots, you’re actually moving about 60 knots ground speed. Whereas, if you have a 15 knot tailwind you would be going about 90 knots ground speed.

One time I was flying (in real life) and the winds were pretty high. My ground speed got down to about 18 knots when I practiced slow flight! It felt like being in a helicopter hovering in the air. However, my airspeed was about 45 to 50 knots. True story.


Picture or it didn’t happen ;)


Although I don’t have a picture of the instrument panel readings, I took several pictures during that flight.


Lmao, I wasn’t expecting this


Thank you very much!

This may sound confusing but I’ll try my best to explain this. If you are going 200kts at sea level, your airspeed will read the same as the ground speed, 200kts. If you were to fly 200kts, at a higher altitude, say 30,000feet, your ground speed may read something closer to 350 or higher. The reason is the lack of air pressure/air density. As altitude increases, air density becomes less. The only way to make up for the lost air density is to increase power to maintain that airspeed which increases your speed over the ground. This is why the ground speed is always higher than airspeed at a cruising altitude when compared to a lower altitude. It would be challenging to give a definitive answer on how to calculate the GS from airspeed unless you are speaking in terms of wind. Then you would either add for a headwind, the wind velocity onto your groundspeed or subtract for a headwind.


Air density has nothing to do with ground speed. As you get higher up, you get farther away from earth and because of this, you need to cover more of an area than you would have to if you were closer to the ground. Think of it as if you were running around a track. The people on the outside of the track have to run a longer distance than the people on the inside of the track so if they run at the same speed, the person on the inside will seem to be running faster when in reality, it is due to the decreased distance. This is the reason that the people on the outside of the track start farther up than the people on the inside of the track. The same applies in our situation.


IF doesn’t calculate ground speed correctly, but if you want to figure out your exact ground speed in straight and level flight, subtract you headwind or add your tailwind component from your airspeed and it will give you your groundspeed.

I’ve noticed multiple times that IF gives me a groundspeed that is 30kts off of what the correct groundspeed would be.

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You might want to check your facts there little buddy…

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So based on that logic that you just explained, you validated my point. If what u are saying is true then our airspeed would be unrealistic. What I said, is not an opinion. It’s fact. With over 600 hours under my belt in real world flying, I think I have an idea of how air speed relates to the computations for ground speed. You may want to check your facts there son.


I’m going to need to see proof that air density effects ground speed. Never heard of that and I already took a college level advanced aerodynamics.

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This is like first grade science that shows you object A has to travel a longer distance to fully orbit the earth than object B does. It is the same way for aircraft. Although you might not notice the difference, there is a difference, no matter how small it is. Object A will need a greater airspeed to maintain the same groundspeed as object B because object A must travel a greater distance.

Again, air density has nothing to do with groundspeed. I have no clue where you pulled that from.


In simplest terms: to maintain an indicated airspeed of 250knots (for example) as you climb through altitudes, your groundspeed will increase. The higher you are, the lower the density. As a result, you are able to physically travel through the air faster. As a result of this, your groundspeed also increases dramatically.

I’m not going to go through and explain it better here, it’s been done 10 times before. I’m not sure which ‘college course’ you did but it seems like you’ve misunderstood a lot of it. Simple maths will suggest that you aren’t getting a 300knot difference in indicated airspeed to groundspeed just because you are 35,000feet above the surface.

Your theory about being further from the earth surface, whilst it may have some tiny effect, is quite inaccurate (remember how large the earth is - go google the degree of the earth slope over a distance of say 40km). All it actually means is, if you are further from the surface of a rounded object, you will need to travel at a higher true airspeed to maintain the the same groundspeed as the lower aircraft. It doesn’t actually mean you will have a higher ground speed just because you are further away.

Use your explanation of a running track as an example. If I’m on the outside lane, running at 10/h, and you’re on the inside lane running at 10 km/h, we are going the same speed. The curve doesn’t mean anything. It’s the manual input from each person that causes the speed. All it means is if I want to reach the finish line as the same time as the inside lane, I have to physically run faster - there is no actual outside physical effect. If I’m in an aircraft, I’m not magically going faster - the aircraft frame doesn’t know my groundspeed, it only knows my airspeed.

What your theory says is actually the opposite to what you are trying to prove! If the air density and winds aloft are exactly the same at 2000 feet and 40,000feet (which they aren’t, but let’s imagine they are)… if we are both travelling at 250 knots indicated airspeed, then due to the slight earth curvature, the aircraft further from the earth would have the slower groundspeed!

Get you an E6B learn how to use it and there your go problem solved. There are a lot of formula’s to compute to get the correct answer and you also need to know the correct values to do it. Converting IAS to TAS, getting your wind correction angles, then computing you GS based on the relative information. The E6B or any other flight computer is the easiest way, but if you want to do it the long way google the formula’s.


Are you serious? You just said the same exact things as I did. You’re saying that the density of the air causes you to travel faster because there is less drag and what I said is if the airspeed were to remain the same between object A and B, the object closer to the earth is going to appear to be moving faster. You’re telling me I’m wrong but you’re reiterating exactly what I said. I also said the difference might not be noticed, but there is a difference. You just said the same exact thing. @GHamsz please read through this and educate someone.

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IAgain, please go and check your facts before you call me the ‘idiot’… it’s actually comical your explanation and what you seem to think are facts.

Go try a simple experiment - fly at 200 knots IAS at 2000 feet, and take note of your groundspeed.

Then, Fly at 200 knots IAS at 20,000 feet, and take note of your groundspeed.

You are arguing that air density has no factor in regards to groundspeed, and that it’s solely related to the proximity to the ground and curvature of the earth.

If your theory is correct, then the aircraft you fly at 2000 feet should have a higher groundspeed than the one at 30,000 feet.

Please, I beg you to go try this, then we’ll determine who’s the ‘idiot’

The lower air density is what allows you to reach higher ground speeds!

In fact, I’ve done you the courteousy of doing it myself.

Firstly, learn the different between indicated airspeed, and true airspeed.

Now, indicated airspeed of 250 knots at 5,000 feet… look at the groundspeed:

Now, same indicated airspeed of 250 knots, but at 20,000 feet… look at the groundspeed:

You just spent the last few posts telling me that the object closer to the earth, will travel faster along the ground.

Now as I’ve said, time and time again, if the air density was no factor (like you claim), then you would be correct. However I have just shown you that the air density IS A FACTOR, and this is why I am
Able to produce a much, much higher groundspeed by holding the same indicated airspeed at a higher altitude!

The earth curve probably does have a factor, but it’s likely to be holding my groundspeed at 20,000feet slower by say 1 knot. It’s far outweighed by the fact that the air density is lower, allowing my groundspeed to increase as I had the same indicated airspeed.

Your entire original argument, was that air density has ZERO factor in what groundspeed you travel at, and that it is solely to do with which object is closer to the earth, thus having a ‘tighter corner’ to travel in. Don’t forget your original argument, stop trying to change it around now.