There is not set rule as to a measurement. It depends on the pendants you choose and whether the pendants are being used for task lighting or accent lighting. For task lighting a general guide is 30" apart. Measure the width of the surface the pendants will be hanging over. Divide in half to find your center point. Place outside pendants approximately 2' from edges of surface. Place remaining pendants evenly at 30" - 36" intervals. 30" or less if pendants are to be used as task lighting.