The right chair height helps prevent cramping and stiffness in your legs, and lets your spine assume its normal shape. Sit on your chair with your feet flat on the floor. Adjust the height of the seat so that your thighs are parallel to the floor, with your knees making a right angle. If not, the seat is too long. Then the seat s too short.
People have different length legs, but most chairs have no way to adjust the depth of the seat.
Don t ignore the problem, though. If you sit on the front of a too-long seat, you won t get proper back support. If you slide back, however, the forward edge of the seat will hit the back of your knees, which can impair circulation. Instead, place a cushion of the right thickness between your body and the chair back, to move you forward a bit. In a too-short seat, your knees tend to drop, pulling your pelvis into an undesirable position.