Fast, accurate electrical calculators for wiring, conduit, load planning and power systems — built for the field.
Every tool shows the working behind its answer — the code table, the formula or the trade constant — so you can check the number instead of trusting it. Works on a phone, on a bad connection, in a basement.
Start with a calculator
- Load & ProtectionVoltage Drop CalculatorPercentage drop over a run, and the size that brings it back in.
- Sizing & SelectionWire Size CalculatorMinimum conductor for a load, accounting for distance and drop.
- Load & ProtectionAmpacity CalculatorCurrent-carrying capacity of a conductor after temperature and bundling derating.
- InstallationConduit Fill CalculatorCross-sectional fill percentage against the Chapter 9 Table 1 limits.
- Load & ProtectionResidential Load CalculatorMinimum service size for a single-family dwelling, by the NEC optional method.
Browse all calculators
18 calculators, grouped by what you are working out.
Sizing & Selection
- AWG Wire Size CalculatorConvert between AWG, kcmil and mm², and find the conductor area for a given size.
- Transformer Sizing CalculatorStandard kVA for a connected load, plus primary and secondary full-load current.
- Grounding Conductor Size CalculatorGrounding electrode conductor from 250.66, or equipment grounding conductor from 250.122.
- Wire Size CalculatorMinimum conductor for a load, accounting for distance and drop.
- Cable Size CalculatorMetric · UK & AUMetric cable sizing in mm², by current rating and mV/A/m voltage drop.
Load & Protection
- Ampacity CalculatorCurrent-carrying capacity of a conductor after temperature and bundling derating.
- Breaker Size CalculatorNext standard overcurrent device rating for a continuous or non-continuous load.
- Residential Load CalculatorMinimum service size for a single-family dwelling, by the NEC optional method.
- Motor FLA CalculatorNEC table full-load current for a motor, with the conductor and breaker sizes it drives.
- EV Charger Circuit CalculatorBreaker and wire size for a Level 2 EV charger, with the mandatory 125% factor.
- Heat Pump & HVAC Circuit CalculatorWire and breaker for AC or a heat pump, from nameplate MCA and MOCP under Article 440.
- Voltage Drop CalculatorPercentage drop over a run, and the size that brings it back in.
Installation
- Conduit Fill CalculatorCross-sectional fill percentage against the Chapter 9 Table 1 limits.
- Box Fill CalculatorVolume allowances for conductors, devices, clamps and grounds against a box’s capacity.
- Conduit Bending CalculatorTrade mathOffset, stub-up and saddle marks, with shrink and take-up worked out.
Power Quality & Backup
- Generator Sizing CalculatorStandby powerBackup generator watts for a load list, including the largest motor starting surge.
- Solar Battery Bank CalculatorDC storageDC storage capacity from daily energy use, autonomy, depth of discharge and losses.
- Power Factor Correction CalculatorFacility powerCapacitor bank kVAR to hit a target power factor, and the kVA demand it saves.
Why these tools
Most of these calculate against theNational Electrical Code (NFPA 70)— conductor properties from Chapter 9 Table 8, ampacity from Table 310.16, conduit dimensions from Chapter 9 Table 4, standard device ratings from 240.6(A), and the grounding tables in Article 250.
A few deliberately do not, and those say so on the page. Conduit bending is geometry and shop practice, with no code opinion about where you put your marks. Generator, battery-bank and power-factor sizing are engineering and commercial decisions the code does not make for you. Where a calculator rests on trade practice or a manufacturer’s list rather than on a published table, it tells you which — because the two deserve different amounts of trust.
Every constant in the source carries a comment naming the table it came from, and each page prints that table underneath the calculator so you can verify the result by hand. Where a rule has an exception we say so rather than rounding it away.
Code adoption is local, and jurisdictions lag editions or amend them. These tools are a planning aid and a check on your own arithmetic — not a substitute for the edition your AHJ has actually adopted.