This tool calculates the antenna capacitance and radiation resistance of small vertical monopoles at 475 kHz. It is by no means a replacement for antenna design software such as EZNEC, but should give a clue how the antenna will perform. Following limitations apply:
Total dimension (H+L) less than 15% of the wavelength (= less than 95 m)
Wire or small tube construction (less than 2.5 cm)
The calculations assume an unobstructed antenna. Object near or under the antenna will reduce the radiation resistance and increase the antenna capacitance.