Electrical calculators that cite the code

Voltage drop, wire size, conduit fill, ampacity and Ohm's law, built on NEC and CEC tables. Free on the web, offline in the Wirewright app for iPhone and Android.

Voltage drop calculator

Full voltage drop calculator with formulas and examples →

Calculators

Voltage Drop CalculatorFree voltage drop calculator for copper and aluminum wire, single or three phase. Uses NEC Chapter 9 Table 8 resistance and checks the 3% / 5% limits.
Wire Size CalculatorFind the right wire gauge for any load. Checks NEC 310.16 ampacity, 240.4(D) small-conductor limits, 125% continuous loads and voltage drop.
Conduit Fill CalculatorFree conduit fill calculator for THHN in EMT, PVC Schedule 40 and RMC. Uses NEC Chapter 9 Tables 1, 4 and 5 and finds the smallest conduit size.
Ohm's Law CalculatorEnter any two of voltage, current, resistance or power and get the other two instantly. Includes the Ohm's law wheel formulas and worked examples.
Amps to Watts CalculatorConvert amps to watts for DC, single-phase AC and three-phase circuits, with power factor. Formulas, a quick reference table and worked examples.
3 Phase Power CalculatorCalculate three-phase kW, kVA and current from line voltage, amps and power factor. Explains the √3 factor with 208 V and 480 V examples.
kVA CalculatorConvert kVA to amps and amps to kVA for single-phase and three-phase systems. Includes transformer full-load current examples and a reference table.
3 Phase Voltage Drop CalculatorVoltage drop calculator for balanced three-phase feeders at 208, 240, 480 and 600 V. Uses VD = √3 × I × R × L / 1000 with NEC resistance values.

Charts & tables

Guides

Voltage Drop FormulaThe voltage drop formulas electricians use: resistance method and K-factor (circular mil) method, single and three phase, with worked examples.

Canada (CEC)

Why Wirewright

Most calculator sites give you a number with no source. Wirewright shows the formula, the table it used and the limit it checked, so you can explain the result to an inspector or a customer. Resistance comes from NEC Chapter 9 Table 8, ampacity from Table 310.16 with the 240.4(D) small-conductor limits, and conduit fill from Chapter 9 Tables 1, 4 and 5. Switch to CEC and the app applies Canadian limits instead.

The app works with no signal in a basement or a new build, remembers your defaults, and with Pro saves calculations to a job history you can export as a PDF.

Frequently asked questions

Are these calculators free?

Yes. Every calculator on this site is free with no sign-up. The Wirewright app is free too; an optional Pro upgrade adds saved job history and PDF export.

Which code editions do the calculators use?

NEC values come from Chapter 9 Tables 1, 4, 5 and 8, Table 310.16 and 240.4(D), which have been stable across the 2017–2023 editions. Canadian pages apply CEC Rule 8-102 voltage drop limits and Rule 12-910 conduit fill limits.

Do the website and the app give the same answers?

Yes. Both run the same calculation code, so a result on wirewrightapp.com matches the app exactly.

Can I rely on these results for an inspection?

They are a reference to help you design and check work. The adopted code edition, local amendments and the authority having jurisdiction always govern.