NEC-referenced
Electrical calculators that show their work
Voltage drop, conduit fill, wire sizing, ampacity, box fill, breaker sizing and IEC cable size. Every answer comes with the formula and the substituted values. NEC results also cite the section they came from. You can check it, save it and print it.
- Calculators & charts
- 14
- Formula shown with the result
- Every tool
- Calculation inputs sent to our servers
- None
Tools
8 calculators and 6 reference charts
Voltage Drop CalculatorSingle- and three-phase drop, checked against the 3% feeder or branch-circuit recommendation.Conduit Fill CalculatorFill percentage against the Chapter 9 Table 1 limit, with the next trade size up when it does not fit.Ampacity CalculatorApplies the ambient, conductor-count and termination corrections to the base table.Wire Size CalculatorFinds the smallest conductor that still carries the load after every correction.Box Fill CalculatorTotals the 314.16 volume allowances and compares them with the box volume.Breaker Size Calculator125% for continuous loads, then up to the next standard overcurrent device rating.Recessed Lighting CalculatorFixture count, grid and spacing from the target illuminance and lumens per fixture.Wire Size ChartAWG and kcmil sizes with circular-mil area, THHN cross-section and ampacity columns.Wire Ampacity ChartBase copper and aluminum ampacities at 60°C, 75°C and 90°C.Conduit Fill ChartMaximum THHN conductors per EMT trade size at the 40% fill allowance.NEC Ampacity ChartThe four reference tables behind every ampacity answer, in one place.IEC Cable Size CalculatorMetric cable size from IEC 60364-5-52 for the installation method, insulation and loaded conductors.mm² to AWG ChartNominal metric sizes beside the nearest AWG or kcmil, with the area difference shown.Quick ReferenceOne page of conductor areas, ampacity, conduit fill and correction factors.
Wire size by circuit rating
Jump straight to the conductor size for a given circuit rating, computed with 60°C terminations for ratings up to 100 A and 75°C above 100 A, 30°C ambient, and three current-carrying conductors. Verify actual equipment and terminal ratings.