Basic Electrical Calculators
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Electrical Calculators & Unit Converters
Electrical Calculators & Unit Converters
NEC-referenced (NFPA 70, National Electrical Code) calculators covering Ohm's Law, power, current, voltage, energy cost, unit conversion, and component decoding.
Who This Is For
This category answers circuit values and component values. Ohm's Law, power, energy cost, and power factor sit next to the resistor, capacitor, and LED tools, because a number from a formula still has to become a part. The pages that cite the code are NEC-referenced (NFPA 70, National Electrical Code). None of these twelve sizes a feeder or a conduit. That work is in Advanced Electrical Calculators. None of them converts a statampere or an abohm. That work is in the unit converters.
Use the search box for a name, or read how the twelve fit together.
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Ohm's Law is the hub of this category. It solves voltage, current, resistance, or power from any two of those. Amps to Watts and Watts to Amps keep the same relationship and add single-phase and three-phase forms, plus a published equipment table. Use the table as a check against a nameplate, not as the nameplate. Power Factor is the reason a watt figure and a volt-ampere figure are not interchangeable. If the power factor is left at 1.0 on a motor load, the current comes out low.
The resistor color code decoder turns bands into ohms and tolerance. The series and parallel calculator turns several resistors into one equivalent. The voltage divider uses two resistors to set an output voltage, and it shows the nearest standard values after a calculation. The capacitor calculator reads a three-digit code and combines capacitors in series or parallel. Capacitor discharge time follows the exponential RC curve and can solve for the bleeder resistor. The LED resistor calculator sizes the series resistor from supply voltage, forward voltage, and current, then shows dissipation so the wattage rating can be chosen above that heat.
A color code does not tell you the power the resistor will dissipate. An equivalent resistance does not tell you the color bands to buy. Move from one tool to the next instead of asking one page to do both jobs.
The kilowatt-hour calculator turns watts, hours, and days into energy. Electrical Cost applies the rate that is typed in. Neither tool knows the utility tariff. A cyclic load such as a refrigerator does not draw its nameplate watts every minute it is plugged in. The appliance tables on those two pages are typical published values, and each row can be copied into the calculator. The comparison form on the cost page stays closed until it is opened, because it is a second calculator rather than a reference list.
Suppose the job is one LED on a 12 volt supply. Start with the LED resistor calculator, not the color code. The calculator returns a resistance and a dissipation. Then open the color code decoder to read a part in that resistance, or the ohms converter to see the nearest standard value. If the same supply also feeds a resistor divider for a sensor, the voltage divider is a separate page. Ohm's Law is the check when two of voltage, current, and resistance are known and the third is not. Putting those steps on one page would hide which formula applied.
When the current from Watts to Amps is for a long run or a motor, stop. The advanced wire-gauge and voltage-drop pages take that current as an input. This category produces the load current. The advanced category asks whether the building can carry it.
Stay on this page when the unknown is volts, amps, ohms, watts, a component value, or a bill estimate. When the unknown is whether the wire, the breaker, or the conduit can carry that current, open Advanced Electrical Calculators. When the unknown is only the unit prefix, or an older unit name on a drawing, open Electrical Unit Converters. The ohms converter is not a second Ohm's Law page. It changes the scale of a resistance and lists standard resistor values.
Print a result that has to leave the screen. Then check the nameplate, the datasheet, and, where the work is installed wiring, the adopted edition of the National Electrical Code (NFPA 70). EnterPlanet LLC operates the site from Jacksonville, Florida. Contact is the form if a formula looks wrong.