The citrus fertilizer calculator will guide you with applying the proper amount of fertilizer for your citrus tree, based on the percentage of nitrogen in the fertilizer.
It is calibrated for the needs of various citrus varieties commonly grown in residential settings in the Arizona low desert regions of Phoenix (Maricopa County) and Yuma (Yuma County). For these purposes the recommendations given will likely prove more accurate than those printed on the fertilizer bag.
Note that the amount and timing of fertilizer application will vary depending on the size and type of citrus tree.