Power Calc Tools
Electrical engineering calculators for feeders, branch circuits, load, power factor, and transformers. Built around NEC 2023 and IEC 60364, with clean UI and mobile support.
Voltage Drop Calculator
LiveNEC 2023 and IEC 60364-5-52. Vd %, pass-fail, minimum-size recommendation.
Cable Sizing Calculator
LiveNEC 310.16 ampacity with temperature + bundling derating, 125 % continuous, OCPD, EGC and voltage-drop check.
Electrical Load Calculator
LiveDwelling service sizing per NEC 220.82 optional method, with service-entrance conductor.
Power Factor Correction
LiveCapacitor bank kvar, µF per phase and current reduction, with a live power triangle.
Transformer Sizing
LiveStandard kVA, FLA, secondary fault current vs AIC, and NEC 450.3(B) protection.
Frequently asked questions
Who are these calculators for?
Electricians, contractors, facility engineers and homeowners planning electrical work. Typical uses: sizing wire for a garage, shop or EV charger run, checking whether a 100 A service can take an EV charger or hot tub, sizing a feeder or transformer for new equipment, and working out a capacitor bank to remove a utility power factor penalty.
Which calculator should I start with?
Follow the order a design follows. Load Calculator: how big the service needs to be. Cable Sizing: the conductor, breaker and grounding conductor for each circuit or feeder. Voltage Drop: whether that conductor is still large enough over the real length. Transformer Sizing: kVA, currents, protection and fault current when you add a transformer. Power Factor Correction: capacitor kvar when the utility bills for low power factor or you need to free capacity.
Are the calculators free? Do I need an account?
Free, with no account, signup or usage limit. Calculations run in your browser. Every input is stored in the page URL, so Copy link gives a link that reopens the exact calculation for a colleague, an inspector or your own records.
Which code editions do the calculators follow?
NEC 2023 (NFPA 70) for all five calculators, with IEC 60364-5-52 as a second mode in the voltage drop calculator. Each result shows the tables and sections it used. Canadian 347 V and 600 V systems are available in the voltage lists, but the conductor data is from the NEC, not the Canadian Electrical Code. The NEC 2026 edition moves dwelling load calculations to a new Article 120; most jurisdictions adopt new editions years later, so check which edition your AHJ enforces.
Can I use the results for a permit or a stamped design?
Use them to plan, check and document your work: every result lists its assumptions and the code basis, and the load calculation copies as an itemized worksheet. They do not replace the judgment of a licensed electrician or professional engineer, and the Authority Having Jurisdiction (AHJ) has the final say on code interpretation — for example how EV chargers are counted in a load calculation.
How are the calculations checked?
Each calculator has reference cases worked out by hand from the cited NEC tables (for example 240 V, 2 AWG copper, 150 ft, 100 A at 0.85 PF gives 6.00 V from Chapter 9 Table 9). Those cases run as automated tests on every change, and a change to calculation code or table data cannot be deployed without a hand-verified test that cites its source.
Suggestions, or spotted an error?
Tell me which calculator you’d like next, or flag a result that looks off — paste the page link and every input comes with it. Leave your email and I’ll get back to you.