The standard distance of planting for fruit trees (citrus included) is 4 x 4 meters, in flat level land or 8 x 8 meters for rolling lands mountainous areas. This distance is only applicable if you don't have other crops planted in between the citrus plantation.
If you intend to apply multiple cropping system, meaning planting different crops in between your citrus orchard, you can adjust the distance to give way to other crops for possible overshading and sunlight and nutrients competition.
