Electrical & NEC Tools
Electrical Calculators
Conduit fill, wire size, box fill, voltage drop, grounding, motor and dwelling loads — every CalcPoint electrical tool in one place, each backed by the actual National Electrical Code tables and a worked example.
These calculators are built for the people who do the work: electricians sizing a feeder on the job, estimators checking a panel schedule, apprentices studying for the license exam, and inspectors double-checking a box fill. Every tool shows the NEC table or formula behind the answer instead of hiding it, so you can trust the result and explain it.
The code calculators below follow the 2020 National Electrical Code (with notes where the 2023 edition renumbers a section). Always confirm against the edition your local jurisdiction has adopted.
NEC Code Calculators
Check NEC conduit fill for EMT, PVC Schedule 40, and rigid metal conduit. See how many THHN/THWN conductors fit under NEC Chapter 9, Table 1.
Find the minimum copper or aluminum wire size for a given load using the NEC Table 310.16 ampacity values, with the 240.4(D) small-conductor rule applied.
Calculate the required electrical box volume under NEC 314.16. Counts conductors, devices, clamps, and grounds to tell you if your box is large enough.
Find the minimum equipment grounding conductor size from the overcurrent device rating using NEC Table 250.122, for copper or aluminum.
Calculate voltage drop across a wire run based on source voltage, current, wire length, and wire gauge.
Look up three-phase motor full-load current from NEC Table 430.250, plus the 125 percent conductor ampacity and 250 percent maximum breaker size.
Size a single-family dwelling electrical service using the NEC standard calculation method (Article 220, Part III), with the Table 220.42 lighting demand factors, Table 220.55 range demand, and the noncoincident heating and cooling rule.
Size a one-family dwelling service the fast way using the NEC optional calculation method (220.82): 100 percent of the first 10 kVA of general load plus 40 percent of the rest, then the largest heating or cooling load.
Electrical Basics
Calculate voltage, current, resistance, or power using Ohm's Law. Enter any two known values to find the others.
Calculate the electricity cost of running any appliance based on wattage, usage hours, and your electricity rate.
Calculate the BTU (British Thermal Units) needed to heat or cool a room based on size, insulation, and sun exposure.
Decode 4-band resistor color codes to find the resistance value and tolerance range.