The Electrician's Calculator has useful equations for electricity and wiring.  These include Voltage Drop equations, Electrical Cost equations, and equations for the relationships between potential (voltage), current, resistance and power (aka Ohm's Law).  Checkout the new Electricians Labor Estimates Calculator!

General Functions

The Electrician's Calculator has a tab for General functions.  These include:

• Voltage Drop calculates the drop in volts over a line based on key measurements including distance, gauge, current, temperature and materials. (e.g. 8.92 volts reduction)
• Voltage Drop % which calculates the voltage drop as a percent of voltage. (e.g. 13.2% voltage reduction)
• Wire Gauge Choice computes the lightest gauge of wire to limit the voltage drop over the distance. (e.g. Gauge: 12 Drops: 9.2%)  VIDEO INSTRUCTION
• Electricity Cost estimates the cost of running an electrical appliance based on key measurements. Note: A recent survey indicated that the average rate for a kiloWatt-hour in the United States was 11.88 cent per kWh (2012)   (e.g. $4.25)
• Rolling Offset computes the travel (T) and run (R) of a rolling offset used in conduit piping based on the offsets and angles. VIDEO INSTRUCTION

Ohm's Law

Ohm's Law established relations between potential (voltage), current, resistance and power. 

Compute Electrical Power: (watts, milliwatts, kilowatts, horsepower)

• Power (P) = I • V:  computes the power (watts) as a function of current (amps) and potential (volts).
• Power (P) = R • I²:  computes the power (watts) as a function of current (amps) and resistance (ohms).
• Power (P) = V² / R:  computes the power (watts) as a function of potential (volts) and resistance (ohms).

Compute Electrical Potential: (volts, millivolts) 

• Volts (V) = I • R :  computes the potential (volts) as a function of current (amps) and resistance (ohms).
• Volts (V) = P / I : computes the potential (volts) as a function of power (watts) and current (amps).
• Volts(V) = √(P • R): computes the potential (volts) as a function of power (watts) and resistance (ohms). 

Compute Electrical Resistance: (ohms, milliohms, kiloohms)

• Resistance (R) = V²/P : computes the resistance (ohms) as a function of potential (volts) and power (watts).
• Resistance (R) = P / I² : computes the resistance (ohms) as a function of power (watts) and current (amps).
• Resistance (R) =  V / I : computes the resistance (ohms) as a function of potential (volts) and current (amps).

Compute Electrical Current: (amps, milliamps, microamps, gilberts)

• Current (I) = V / R : computes the current (amps) as a function of potential (volts) and resistance (ohms).
• Current (I) = P / V : computes the current (amps) as a function of the power (watts) and the potential (volts).
• Current (I) = √(P/R): computes the current (amps) as a function of the power (watts) and the resistance (ohms).

User Notes

Feel free to update this section with advice, data and references for people using these equations.