NEC field calculators
The everyday code math, done in your browser. Free, no app install, no signup. Built on the same NEC tables you'd reach for on the job.
Voltage Drop Calculator
Most usedSize a run for the 3% drop rule: enter voltage, current, distance and wire size and get the exact voltage drop and percentage.
Open calculatorWire Size / Ampacity Calculator
Table 310.16Find the smallest conductor that carries your load using NEC Table 310.16, with the 60/75/90°C column and the 240.4(D) small-conductor cap applied.
Open calculatorConduit Fill Calculator
Chapter 9Check whether your conductors fit: EMT, PVC or rigid, with the 53/31/40% Chapter 9 fill rule done for you.
Open calculatorBox Fill Calculator
314.16(B)Total the cubic-inch volume of a device box per NEC 314.16(B): conductors, devices, clamps and grounds.
Open calculatorThese calculators use long-standing NEC values (Chapter 9, Table 310.16, 314.16) that are stable across the 2017-2023 editions for the sizes shown. They're estimating aids for planning. Always verify the final design against the code edition your jurisdiction has adopted. See which edition your state enforces →
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