Fast electrical calculators for electricians, apprentices, foremen, QA/QC, and commissioning techs.
Run quick checks for Ohm's Law, wire ampacity, breaker sizing, transformers, conduit fill, voltage drop, motors, and panel loads. This is a field reference tool, not a stamped engineering design.
Ohm's Law / Power
Enter any two values to solve for the other two.
V = IR | P = VI | P = I²R | P = V²/RWire Sizing & Ampacity
Find minimum wire gauge for a load, or look up ampacity of a known size.
NEC Table 310.12 / 310.16Breaker & Wire Sizing
Size breakers and conductors for branch circuits, feeders, and general loads per NEC.
NEC 210.19 / 210.20 / 240.4 / 240.6Transformer Sizing & Breaker Sizing
Size a transformer from load, find primary/secondary FLA, and size primary/secondary overcurrent protection per NEC Article 450.
NEC Art. 450.3 — Primary & Secondary OCPConduit Fill
Check NEC 40% fill limit for conductors in conduit.
NEC Chapter 9 Tables 1, 4 & 5Voltage Drop
Calculate voltage drop and verify NEC recommendations (3% branch, 5% total).
VD = (K × I × D × factor) / CM | K=12.9 Cu / 21.2 AlMotor Calculations
FLA, overcurrent protection, conductor sizing, and starter sizing per NEC Article 430.
NEC Art. 430 — 125% FLA conductor ruleLoad / Panel Schedule
Calculate service size, total load, and demand load per NEC Article 220.
NEC Art. 220 Standard MethodAdd Loads
How to use this electrical calculator
Pick the calculator from the left menu, enter the known field values, and press calculate. These tools are intended for quick checks while planning, reviewing drawings, commissioning equipment, or sanity-checking common electrical math.
Best use cases
- Quick Ohm's Law and wattage checks.
- Basic copper conductor ampacity lookup.
- Breaker sizing for non-continuous and continuous loads.
- Transformer kVA and overcurrent protection checks.
- Conduit fill and voltage drop estimates.
Field warning
Always verify against the latest NEC, local code amendments, project specifications, engineer direction, manufacturer documentation, and AHJ requirements. This tool does not replace licensed professional judgment.
Common electrical formulas
Ohm's Law: V = I × R. Power is commonly calculated as P = V × I.
Three-phase current: I = VA ÷ (V × 1.732), before power factor corrections where applicable.
Voltage drop: Higher current, longer distance, and smaller conductors increase voltage drop. Upsizing conductors reduces voltage drop.
Continuous loads: Many continuous loads are sized at 125% for conductors and overcurrent protection depending on the application and code section.