https://www.piano-composer-teacher-london.co.uk/post/how-to-sit-properly-on-the-piano

Many piano students encounter the same problem when studying the instrument.

In the beginning, an incorrect body position might pass unnoticeable. Still, when the student has gained more stamina with the piano, if the body position is not correct, this can produce long-term physical problems that are at the very least, undesirable.

All the piano tutors should be aware that insisting on this issue is never a waste of time, and to remind their students constantly is part of a good piano lesson.

But what makes a good posture at the piano?

Firstly, we must take into account where to sit. The best option to sit at the piano is having an adjustable bench. This type of seat allows adjusting the angle of the arm if necessary. Also, both feet should be firm on the ground.

Following the arm position, as Iris Kreiman specifies in her article, “We support the hand on the keyboard, creating a 90º angle on the arm and forearm, making sure that the elbow is at the height of the white keys. If the elbow is above the height of the keys, the chair would be too high. On the contrary, if the elbow is below the height of the key, that would mean the chair is too low.

Another important aspect is the position of the wrists; they should always be straight aligned to the knuckles and forearms, and always above the level of the keys.

Lastly, we arrive at the hand position. The fingers will curl slightly, making the hand naturally rounded. It is at the tip of the fingers, where we will bear all the weight of the back, shoulders and arms.

All these aspects are vital and extremely important to get a correct and proper position at the piano, regardless of the style and level you play. 

If you want to learn more about the correct position, click on the link aforementioned and get to know the ergonomics on the piano.