When calculating even picket spacing, it is important to consider the width of each picket and the desired gap between them. First, measure the total length of the area where you are installing the pickets. Subtract any end gaps or spaces that you want to leave without a picket. Then, divide this adjusted length by the number of pickets you plan to install. This will give you an approximate spacing measurement between each picket. Adjust this measurement slightly if needed to ensure that both ends of the fence have similar-sized spaces.