Free Electrical Calculators
NEC-based calculators and reference tools for working electricians, apprentices, and exam candidates. Every tool is free, runs in your browser, and uses formulas and tables from the 2023 National Electrical Code.
We built these because the calculators we needed on the job site - conduit fill that does not lock the answer behind an account, voltage drop that lets you compare wire sizes side by side, an ampacity chart you can actually filter - did not exist in one place. There are 16 tools below, grouped by what they do.
NEC calculators
Code-driven calculations for sizing, fill, derating, and protection. Each tool cites the NEC article it implements so you can cross-check against the printed code.
Conduit Fill Calculator
FreeCalculate conduit fill percentage per NEC Chapter 9. Select conduit type, size, and wire configuration to verify code compliance.
Voltage Drop Calculator
FreeCalculate voltage drop for any circuit. Verify compliance with the NEC 3% branch circuit and 5% total drop recommendations.
Box Fill Calculator
FreeCalculate electrical box fill per NEC 314.16. Add conductors, clamps, devices, and grounds to verify box capacity.
Breaker Size Calculator
FreeDetermine the correct breaker size for your circuit. Accounts for continuous and non-continuous loads per NEC 240.6(A).
Ohm's Law Calculator
FreeCalculate voltage, current, resistance, and power using Ohm's Law. Enter any two values to find the other two.
Wire Size Calculator
FreeFind the right wire size for your circuit. Accounts for ampacity, temperature derating, bundling, and voltage drop.
NEC Derating Calculator
FreeApply NEC temperature correction and conductor bundling adjustment factors to find derated ampacity.
Transformer Sizing Calculator
FreeSize transformers and calculate overcurrent protection per NEC 450.3(B). Includes primary and secondary breaker sizing.
3-Phase Power Calculator
FreeCalculate three-phase power, current, and voltage. Free calculator for 3-phase electrical systems with power factor.
Unit converters
Convert between watts, amps, volts, kVA, kilowatts, and horsepower for single-phase and three-phase circuits with adjustable power factor.
Electrical Unit Converter
FreeConvert between watts, amps, volts, kW, kVA, and horsepower. Supports single-phase and three-phase calculations.
Amps to kW Calculator
FreeConvert amps to kilowatts instantly. Free calculator for single-phase and three-phase electrical circuits.
Amps to Watts Calculator
FreeConvert amps to watts for any circuit. Free calculator supporting single-phase and three-phase with power factor.
HP to Amps Calculator
FreeConvert horsepower to amps for electric motors. Free calculator with efficiency and power factor for single-phase and three-phase.
kVA to Amps Calculator
FreeConvert kVA to amps for single-phase and three-phase circuits. Free electrical calculator for electricians.
Watts to Amps Calculator
FreeConvert watts to amps instantly. Free calculator for single-phase and three-phase circuits with power factor adjustment.
Reference charts
Filterable NEC tables you can search instead of paging through the codebook.
Frequently asked questions
- Are these electrical calculators really free?
- Yes. Every calculator on this page is free to use, with no signup, no paywall, and no usage limit. They run entirely in your browser. Our paid product is the Texas journeyman exam prep course (question bank, timed simulations, and progress tracking) - the calculators stay free.
- Which version of the NEC do these calculators use?
- Calculations follow the 2023 National Electrical Code, which is the version Texas adopted on November 1, 2023. We are tracking NEC 2026 changes and will update each tool ahead of state adoption.
- Can I use these calculators on a real job site?
- These tools are built to match NEC formulas and tables, but they are reference aids - not a substitute for an authoritative codebook, an engineered design, or your AHJ. Always verify critical calculations against the printed NEC and have inspections signed off by the authority having jurisdiction.
- Do the calculators work on my phone?
- Yes. Every tool is mobile-friendly and works offline once the page has loaded. You can save the page to your home screen for one-tap access from a truck or job site.
- How do these tools help with the Texas journeyman exam?
- The exam includes calculation questions on conduit fill, box fill, voltage drop, ampacity, derating, and motor sizing. Working real problems on these calculators while you study builds the muscle memory you need to solve them by hand on the PSI exam, where you cannot bring a calculator app.
Studying for the Texas journeyman exam?
The calculators above cover the math you will see on exam day, but the Texas journeyman exam is more than calculations. Our paid prep course adds a question bank, timed PSI-format practice exams, and progress tracking that pinpoints the NEC articles you need to review.