The Difference Between AGL & MSL

I’ve seen a lot of confusion from people when determining what the difference is between AGL & MSL. The confusion does not only exist within the IFC, but there are outside cases of this confusion. For people struggling to determine the difference between the 2, I have created a tutorial to eliminate the confusion.


AGL = Above Ground Level
MSL = Mean Sea Level

The purpose of AGL:

AGL is the most commonly used. It references your altitude you are at from the ground below you. So say I am at FL350 above the DFW metropolitan area. My altitude is set at FL350, however the ground above me ranges from 400 to 1300 feet. So that means as I am cruising over the DFW metropolitan area, my altitude will constantly be changing, no matter what I set my altitude at. That is used a lot when flying. The only time you won’t usually be using it is when you are flying in mountainous areas, such as Salt Lake City and Denver.

The purpose of MSL:

MSL, as stated above, is used in mountainous areas. It is also used at higher altitudes, and over seas and oceans. When you are flying over the alps, or Himalayas, oceans, or areas like that, it is important to use MSL. MSL references your FL above the ground below you. When an aircraft has reached an altitude where AGL is harder to use, the pilot will determine his altitude off of MSL.

I hope my tutorial today has helped you understand the difference between the 2 altitude references and when you should use each one. Thanks for taking the time to read this tutorial, and I hope you got something out of this today! Here is a little additional resource to use:
Thanks @Chris_S for the pic.

Happy Flying!


AGL is really important when it comes to flying in mountainous areas. I think you’ve got the two mixed up.

Here’s an example… if you takeoff from KJFK where the airport is 20 feet above sea level, and you’re flying to KDEN, you’re gonna think that you can descend to 3,000 feet and be at a safe pattern altitude, right? Wrong. You’ll actually be in the ground. That’s why you need to figure out what elevation your airport is at, and use that as your reference.


That’s what I thought.

@FlyFi I think pilots will be smart enough to find the elevation of an airport. I think we all know that nobody smart enough is going to descend to 3,000 if they know the altitude is 5400 feet. Just saying.

If they are smart enough to do that then wouldn’t they know the AGL & MSL

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You mean the ground below you ?

Also, I have no idea what you’re saying there at the end of your definition of AGL; I use AGL everytime I fly into a mountainous area. Why would you use MSL and subtract the airport elevation? You’re literally doing the exact same thing that AGL does for you, just in a longer form.

You just contracted yourself. I think you have them confused.


Fixed the typo in the paragraph.


MaxSez. Suggest this Topic be redirected from General to Tutorials @Chris_S.
Regards @Delta_Alpha_Lima, Good Job, BZ;


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Correction: MSL references your altitude in relation to sea level NOT the ground below you.

MaxSez: “Above/Below”! Grammarians they give me gas. It’s really bad form to Correct or Criticize a peer by public comment when they make a technical error or mis-speak while formulating a Topic or making a point. One must keep in mind we are amoung friends/colleagues on this Forum and use a PM rather than demean a peers best efforts in a condescending or superior, I know it all, manner. Just Sayin…

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Sorry I will leave now

Oh yes that’s very helpful because I fly over mountains and then like I have to immediately pull up so I don’t smash into the mountain 🛫⛰
I generally don’t fly at a high altitude

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