These calculators are designed to help you determine the values of the components you'll need for the current transformer(s) used in the Open Energy Monitor project. Go check it out!
Please note these calculators do not take into account core permeability and core AL value. Use at your own risk.
Update November 2017: Fixed formulas displayed below each calculator to halve the system voltage as was originally intended.
burden_resistor = (system_voltage / 2.0) / ((I_RMS * 1.414) / ct_turns)
I_RMS = (((system_voltage / 2.0) / burden_resistor) * Turns) * 0.707
turns = (I_RMS * 1.414) / ((system_voltage / 2.0) / burden_resistor)