Online Calculators and Tables to Help You Determine Proper Wire Size


These online calculators use Ohm's Law to calculate voltage, current, resistance, or watts. Follow the instructions for each calculator below.

Ohm's Law Calculator


Enter two of the values below to calculate WATTS from V, I, or R.






Power (Watts) : -


Enter two of the values below to calculate VOLTS from W, I, or R.






Voltage (Volts) : -


Enter two of the values below to calculate AMPS from W, V, or R.






Current (Amps) : -


Enter two of the values below to calculate OHMS from W, V, or I.






Resistance (Ohms) : -

The following equations are used in the calculators above to derive power, voltage, current, and resistance.

Power Equations:
P = V * I
P = I^2 * R
P = V^2 / R


Ohm's Law Equations:
V = I * R


For long conductor runs where voltage drop may be an issue, use the Voltage Drop Calculator to determine voltage drop and the Circuit Distance Calculator to determine maximum circuit length. Visit the Tables page to view reference tables such as Maximum Ampacity for Current-Carrying Conductors.


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