How do tell your out of tune on an instrument?

There's really not a specific way to judge by ear... If you know it's the wrong note then yeah. But I highly suggest using a tuner. But if the note is lower than you think it should be it's flat. If it is higher than you think it should be then it is sharp.

playing with another saxophone and if your not in tune with each other you cant really point to who is right or wrong. Of course you could keep the tuner on the side and see how your playing, but the best way to keep in tune is to match the person your playing with. The saxophone can not be in tune all the time while playing it, some notes need adjustment in the embrasure (like middle D almost always tends to be sharp so you got lower a little bit in the mouth). Each saxophone is a little different so you should get a tuner and hold notes as you play scales or long tones. So ya, get to know your horn and practice adjusting your embrasure.

When playing with another saxophone, there's no way to tell which one of you is out of tune unless you have perfect pitch (which you and about 99.99% of the world don't). It sounds like you can tell when you're out of tune, you just can't tell whether you are sharp or flat. For starters, just adjust your mouthpiece one way or the other. For example, if you push in and it sounds worse, then you obviously need to pull out. After a lot of trial and error, you'll eventually get the hang of it and be able to make adjustments without even thinking about it.

Usually no one can feel if they are out of tune unless when they play alone unless you have a "perfect pitch" which you have to be born with. Although everyone can develop a "relative pitch" meaning if you have something like a tuning fork and listen to it, your brain can then identify if you are playing in or out of tune.

playing with another saxophone and if your not in tune with each other you cant really point to who is right or wrong. Of course you could keep the tuner on the side and see how your playing, but the best way to keep in tune is to match the person your playing with. The saxophone can not be in tune all the time while playing it, some notes need adjustment in the embrasure (like middle D almost always tends to be sharp so you got lower a little bit in the mouth). Each saxophone is a little different so you should get a tuner and hold notes as you play scales or long tones. So ya, get to know your horn and practice adjusting your embrasure.

When playing with another saxophone, there's no way to tell which one of you is out of tune unless you have perfect pitch (which you and about 99.99% of the world don't). It sounds like you can tell when you're out of tune, you just can't tell whether you are sharp or flat. For starters, just adjust your mouthpiece one way or the other. For example, if you push in and it sounds worse, then you obviously need to pull out. After a lot of trial and error, you'll eventually get the hang of it and be able to make adjustments without even thinking about it.

Usually no one can feel if they are out of tune unless when they play alone unless you have a "perfect pitch" which you have to be born with. Although everyone can develop a "relative pitch" meaning if you have something like a tuning fork and listen to it, your brain can then identify if you are playing in or out of tune.