Free, fast electrical calculators for engineers, electricians and students. Each calculator has built-in US voltages (120 V, 120/240 V, 208Y/120 V, 480Y/277 V) and international ones (230 V, 400 V), works with NEC (AWG) and IEC (mm²) practice, and explains the formula with worked examples.

• Voltage Drop Calculator
  Voltage drop and % drop for copper or aluminum wire in AWG or mm².
• Wire Size Calculator
  Smallest wire that meets ampacity and voltage drop for your load and distance.
• kVA Calculator
  kVA to amps, amps to kVA and kW to kVA, single- and three-phase.
• Transformer Sizing Calculator
  Standard IEC/ANSI transformer rating from your load, with growth margin.
• Breaker Size Calculator
  Circuit breaker rating from amps, watts or kW using NEC or IEC ratings.
• Conduit Fill Calculator
  Smallest EMT, PVC, IMC or rigid conduit for your wires under NEC Chapter 9.
• Generator Sizing Calculator
  What size home or commercial generator you need, with motor starting loads.

Guides that go with these calculators

• How to calculate the electrical load of a house
• How to do a 3-phase electrical load calculation
• Electrical load calculation in building design
• Demand factor and diversity factor explained
• Ics and Icu of a circuit breaker

These calculators give engineering estimates for planning and learning. Final designs must follow your local code (NEC, IEC/BS 7671, PEC or the authority having jurisdiction) and be checked by a qualified electrical engineer or licensed electrician.