Shoulder pads are relatively easy to size, but it is imperative that they fit correctly in order to ensure proper protection of your collarbone, upper chest, back, upper arms and shoulders. To determine the correct size, make sure the center of the shoulders line up directly with the center of the shoulder caps. Measure the circumference of your chest just below the armpits. All shoulder pads will have a corresponding size based on this measurement. Most shoulder pads also have adjustable straps in other areas of the pads; this adjustable fit is acceptable as long as the shoulders and shoulder cups line up correctly.