The calculation of the comsumptive use by crop can be most accurate when it is actually measured. The mankind is not yet able tole grasp all the natural conditions or phenomena. The induces of actual measurement at a representive observatory and the formula abtained from the area werowere made as close as possible, which is called as the Blaney Criddle formcula, published in 1945. In calculating the water require-ment of consumptive use of water by farm crops, a more accurate and reasonable formula should be induced as the factors other than temperature and day-time hours according to the location of project area have also influences. The formula of Mr. Jerald E. Christianen published in 1969 is based on the induces of the records of actural measurements for 3, 928 months at 80 different stations and his formula couers a wider range of functions that calculate water requirement to induce the functions of moisture, wind, velocity, sunshine at elevatons, in addition to temperature and daytime hours in accordance with latitude and was modified to be fit to natural phenomena. The formula is being widely in use in many contries with their modification since it is worth while for usealso in korea, the formula is introduced and explained in the following.