Electrical Calculators
Circuit Power Calculator
Compute apparent, real, and reactive power in an AC circuit from voltage, current, and power factor, with typical power factor reference values shown.
Electric Field Calculator
Find electric field strength from force and charge, or from a point charge using Coulomb's law, with reference field strength comparisons shown.
Electrical Load Calculator
Total appliance loads, apply a demand factor, and convert the result to circuit current draw at a given voltage for panel and circuit sizing work.
Magnetic Field Calculator
Calculate magnetic flux density for a straight wire, the center of a circular loop, or inside a solenoid, with real-world flux density comparisons shown.
Ohm's Law Calculator
Solve for voltage, current, or resistance using Ohm's Law, with a worked numeric example and the full formula substitution shown step by step here.
Resistor Calculator
Combine resistors in series or parallel to find total equivalent resistance, with the underlying formulas and a fully worked numeric example included.
Transformer Rating Calculator
Calculate the required transformer VA rating, turns ratio, and primary current from secondary voltage and current on an ideal transformer setup.
Voltage Drop Calculator
Estimate voltage drop and percent drop across a copper conductor by wire gauge, length, current, and phase, checked against the 3% design guideline.
Wattage Calculator
Calculate electrical power from voltage, current, or resistance in watts, and compare the result against typical household appliance wattage ranges.
Wire Size Calculator
Match load current to a minimum copper wire gauge using a simplified NEC ampacity table, with the 125% continuous-load design rule applied here.
The Formula Behind Every Circuit Decision
Nearly every electrical calculation traces back to Ohm's law — voltage equals current times resistance — but applying it correctly to real wiring means also accounting for wire gauge, run length, and load type, which is where voltage drop and wire size calculations come in. Ten calculators here cover the core formulas used in both circuit design and everyday electrical troubleshooting.
Popular Electrical Calculators
Ten tools span circuit basics, wiring, and equipment sizing:
- Ohm's Law Calculator — solves for voltage, current, or resistance given the other two values.
- Wire Size Calculator — selects appropriate wire gauge for a circuit's amperage and run length.
- Voltage Drop Calculator — estimates voltage lost over a wire run, critical for long circuit lengths.
- Wattage Calculator — converts between watts, volts, and amps for load sizing.
- Transformer Rating Calculator — sizes a transformer's kVA rating to the connected load.
Why Voltage Drop Gets Worse Over Distance
Every wire has resistance, and that resistance scales with length — which is why a circuit that works fine at 20 feet can show meaningfully lower voltage at the load when the same wire gauge runs 100 feet, especially under higher current draw. This is why electrical codes specify maximum recommended voltage drop percentages (commonly 3% for branch circuits) and why longer runs typically need a thicker wire gauge than the minimum ampacity rating alone would suggest, even when the circuit is technically within amperage limits.
Frequently Asked Questions
Why does wire size depend on more than just the amperage?
Ampacity sets a minimum, but run length, ambient temperature, conduit fill, and acceptable voltage drop can all push the required gauge higher than the bare amperage rating would suggest.
Is a higher wattage appliance always a bigger electrical safety concern?
Not directly — what matters for wiring and breaker sizing is current draw (amps), which is wattage divided by voltage, so two appliances at the same wattage can draw very different currents at different voltages.
Explore More
Working with HVAC electrical loads too? See the HVAC Calculators, or check broader physics formulas in the Physics Calculators.