Perfect standing posture is when the following are properly aligned – the points between your eyes, chin, collarbone, breastbone, pubic area and midpoint between your ankles. From the side, you can easily see the three natural curves in your back. From the front, your shoulders, hips and knees are of equal height. Your head is held straight, not tilted or turned to one side. From the back, the little bumps on your spine should be in a straight line down the center of your back.
Obviously, no one spends all day in this position. But, if you naturally assume a relaxed standing posture, you will carry yourself in a more balanced position and with less stress in your other activities.