Stand straight on the floor with shoulders relaxed and lowered. Bend your arm at the elbow at an angle of 90 degrees so that your forearm is parallel to the floor. Measure the distance from your forearm to the floor and use it as the desk height for the standing position.
Sit down on the chair so that your feet are flat on the floor, the knee angle is 90 degrees, your back is straight, and your shoulders are down. Bend your arm at the elbow at an angle of 90 degrees so that your forearm is parallel to the floor. Measure the distance from your forearm to the floor and use it as the desk height for the sitting position.