Electrical calculators that answer on the first screen

Wire size, conduit fill and voltage drop — instant results, no signup, phone-first.

Wire Size CalculatorPick the right AWG for any load, with a built-in distance check. Conduit Fill CalculatorHow many THHN conductors fit in EMT or PVC — at legal 40% fill. Voltage Drop CalculatorCheck any run against the 3% guideline, single or three phase. Wire Size ChartAmpacity by AWG for copper and aluminum at 60/75/90°C.

What these tools do

Every branch circuit raises the same three code questions: what gauge wire can carry the load (NEC 310.16 ampacity, with the 240.4(D) small-conductor limits applied automatically), how many wires legally fit in a conduit (NEC Chapter 9, 40% fill), and whether the run is too long for acceptable voltage drop (3% guideline). TradeCalcs answers all three from one screen, using the same tables an inspector will check against.

Results assume common conditions — 30°C ambient, three or fewer current-carrying conductors, THHN/THWN-2 insulation. High ambient temperatures, bundling, and continuous loads require derating. Always confirm with your local AHJ.

Common quick answers

50 amps at a 75°C termination calls for 8 AWG copper; on a 240 V, 75 ft run that lands at ≈2.4% voltage drop — inside the guideline, while a 100 ft run pushes past 3% and gets upsized to 6 AWG. 3/4″ EMT holds up to 16 × 12 AWG THHN at 40% fill. A 20 A load on 12 AWG copper at 120 V exceeds the 3% guideline past roughly 50 ft one-way — the distance check upsizes the conductor for you.