Electrical Engineering Calculators
These calculators cover power circuits and supply: choosing a conductor size from ampacity tables and voltage drop, converting between kilowatts, kilovolt-amperes and amps on single and three-phase systems, sizing capacitors to correct power factor, picking a transformer, estimating how long a battery or UPS will last, and sizing a solar array or a backup generator.
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All Electrical (7)
Wire Size Calculator
Conductor size for a load from ampacity and voltage dropThree-Phase Power Calculator
kW, kVA and amps for single-phase and three-phase circuitsPower Factor Correction Calculator
Capacitor kVAR needed to raise power factorTransformer Sizing Calculator
Transformer kVA and primary/secondary currents for a loadBattery Runtime Calculator
How long a battery or UPS runs a load, with efficiency and depth of dischargeSolar Panel Calculator
Panels, array size and battery bank for a daily energy needGenerator Size Calculator
Generator wattage from running and starting loads
Which tool do I need?
Pick a wire size for a 40 A circuit
Enter the load, conductor material, insulation rating and run length to get a size that passes ampacity and voltage drop.
Convert a three-phase motor's kW to amps
Enter the power, line voltage, power factor and efficiency to get the line current.
Size a solar system and battery bank
Enter your daily energy use and peak sun hours to get the number of panels and the battery capacity for the days of autonomy you want.
Choose a generator for a home outage
List the appliances with their running and starting watts to get the generator size with headroom.
About Electrical
Ampacity and correction factors follow the NEC tables, with a labelled IEC mode for metric cables. Battery and solar tools account for inverter efficiency, depth of discharge and system losses, which is where most rough estimates go wrong. The Ohm's Law, Voltage Drop and Electricity Cost calculators in the Science & Electronics group complement these.
Results are for checking, learning and preliminary design. Anything that carries load, current, pressure or people must be confirmed by a qualified engineer or licensed tradesperson against the code that governs your project. Electrical installation work is regulated in most places and must be done or inspected by a licensed electrician.
Guides
- How to Size Electrical Wire: Ampacity, Derating and Voltage DropReading NEC Table 310.16 properly: terminal temperature limits, the 125% continuous-load rule, ambient and bundling derating, small-conductor breaker caps and when voltage drop decides the gauge.
- The Three-Phase Power Formula: Where √3 Comes FromWhy three-phase power is √3 × V × I × PF, line-to-line versus line-to-neutral voltage, kW versus kVA versus kVAR, and turning motor horsepower into amps without the usual mistakes.
- Power Factor Correction: Sizing Capacitors in kVAR and µFWhat power factor is, why utilities charge for it, the tan φ formula behind every kVAR table, converting kVAR to microfarads for delta and star banks, and the harmonics trap.
- Transformer Sizing: kVA, Full-Load Amps and Standard RatingsHow to size a transformer from demand load, why ratings are in kVA, primary and secondary full-load current, turns ratio for delta-wye units, and the margins engineers add.
Frequently asked questions
Why do electrical calculators ask for both kW and kVA?
kVA is apparent power, voltage times current. kW is the real power that does work. They differ by the power factor, so a 100 kVA supply at 0.8 power factor delivers 80 kW.
Why does a continuous load need a 125% conductor rating?
The NEC treats loads running three hours or more as continuous and requires the conductor and breaker to be sized for 125% of the current, so they do not overheat over long periods.
How much of a lead-acid battery's capacity can I use?
About 50% for a long service life, while lithium iron phosphate batteries are commonly cycled to 80 to 90%. The battery runtime calculator applies these as editable defaults.
Why does a generator need extra capacity for motors?
Motors draw several times their running current for a moment when they start. The generator must cover the largest starting surge on top of everything else that is running.