Electrical Calculators
Free NEC Electrical Calculators
Organized by the job: adding a big load, sizing wire and breakers, running conduit, and which NEC edition your state enforces. Under each job the calculators, charts, and guides are labeled so you grab the right kind fast. Every code result names the NEC table it used.
Adding a big load? Panel & service capacity
An EV charger, heat pump, water heater, or induction range comes down to one question: can the service take it, and if not, what is the workaround? Start here.
Can My Panel Handle It?
Adding an EV charger, heat pump, water heater, or induction range? Pick the load and get the exact calculator, plus the NEC 220.87 check and the workarounds that add it without a service upgrade.
Electrical Load Calculator
NEC 220.82 service sizing and the 220.87 existing-load check. Answers the question behind every electrification job: can this panel handle an EV charger or heat pump?
Runs in your AINewTap Conductor Calculator
Feeder taps under NEC 240.21(B). Picks the rule your run falls under, shows the ampacity floors it sets and which one governs, and sizes the conductor from Table 310.16. The 10 ft rule is not one-tenth by default.
Sub-Panel Wire Size Calculator
Feeder conductor, equipment ground, breaker, conduit, and voltage drop for a 60-200A sub-panel per NEC Table 310.16 and 250.122, plus the 4-wire feeder and neutral-isolation rules that pass inspection.
EV Charger Installation Calculator
Size wire, breaker, and panel capacity for Level 2 EV charger installations per NEC 2023 Article 625. Includes GFCI requirements, charging performance, and a parts list for the circuit itself.
Runs in your AIEV Load Management (Biggest Charger)
The biggest EV charger a service can take by NEC 220.87, and how a load-management device (DCC, Emporia, Wallbox Power Boost, Splitvolt) raises it without a panel upgrade.
Runs in your AIHeat Pump Water Heater Circuit
Breaker and wire size for every major heat pump water heater line, 240V hybrids and the new 120V plug-in class, plus the NEC 210.23(B)(2) shared-circuit rule.
Runs in your AI120V Induction Range Circuit
Can a battery-buffered 120V plug-in induction range (Copper, Impulse, Electra) share a circuit? The breaker, wire, and NEC 210.23(B)(1), sized from the wall draw not the burner kW.
Runs in your AICan My Panel Handle Solar?
The max solar backfeed breaker your busbar can take by the NEC 705.12 120% rule: 120% of the bus less the main, rounded down to a standard size, with the inverter output it supports.
Runs in your AISizing the heat pump first? Cold-climate heat pump capacity at 5F.
Sizing wire, breakers & circuits
Wire Size Calculator
Find the correct wire gauge per NEC 310.16 with temperature derating, bundling adjustment, continuous load support, and NEC 110.14(C) terminal temperature enforcement.
Runs in your AIVoltage Drop Calculator
Calculate voltage drop percentage for any circuit run length. Includes reverse-solve to find the minimum wire size that meets NEC 3% branch / 5% total recommendations.
Runs in your AIMCA & MOCP Breaker Calculator
What breaker and wire does this condenser need? Enter the nameplate MCA and MOCP and get the wire size, breaker, ground, and voltage drop per NEC Article 440.
Runs in your AINewTransformer OCPD Calculator
Transformer protection under NEC Table 450.3(B). Shows the cell that applies, the percentage ceiling it sets, and which way that cell rounds. The 250 percent primary rounds down: Note 1 is scoped to 125 percent and does not reach it.
NewThree-Phase Motor Calculator
Conductor and maximum inverse-time breaker for a single motor, from horsepower and voltage per NEC Table 430.250. Sized from the table full-load current, never the nameplate: 430.6(A)(1) is explicit, and the nameplate sizes only the running overload device.
NewIs the Neutral a Current-Carrying Conductor?
NEC 310.15(E) has exactly three printed branches and which one you are in decides it. A 120/240V three-wire neutral is not covered by (E)(2), because (E)(2) is scoped to a wye. Counts the whole raceway, including pulled spares, and carries the count through the adjustment to a conductor size.
NewNEMA Plug & Receptacle Identifier
Identify a plug or receptacle from what you can see, without knowing the designation: straight blade or twist-lock, how many slots, whether one is a ground pin. 10-30 and 14-30 are both 30A at 125/250V and only one has an equipment ground, so grounding is printed as its own answer.
Guides & answersWhat size breaker do I needWhat size ground wireHow many amps does an appliance useHow many outlets on a circuitWire size for appliancesMini split breaker sizeMrCool mini split breaker sizeA2L (R-454B) changeout circuit checkCopper vs aluminum wireTHHN vs THWN
Conduit, bending & boxes
Conduit Bending Calculator
Calculate bending marks for every bend family the calculator carries and see each as an interactive 3D rendering or flat diagram: offset, rolling offset, 3-point saddle, 4-point saddle, 90 stub, back-to-back 90s, kick with 90, parallel offset, parallel kick (sideways and forward), matching bends and centers across two sizes, the segmented 90, the compound 90 around an obstruction, and whole sticks of many bends on one conduit.
Runs in your AIConduit Fill Calculator
Check NEC Chapter 9 conduit fill compliance for any mix of conductors. Supports EMT, IMC, RMC, PVC Schedule 40/80, and ENT with nipple exception.
Runs in your AIBox Fill Calculator
Calculate junction box fill per NEC 314.16 including conductors, device yokes, internal clamps, equipment grounding conductors, and terminal blocks.
Runs in your AICharts & NEC tablesConduit fill chart (THHN/EMT)Offset multiplier chart90 degree deduction chart
Guides & answersWhat size conduit for a wire pullConduit types (EMT, PVC, RMC, more)
Which NEC year applies? Editions & adoption
Which edition your jurisdiction enforces, what changed, how the load calc differs between 2023 and 2026, and whether the listed-HVAC GFCI exception still exists where you work.
Guides & answersNEC 2026 changesNEC 2023 vs 2026 load calculationNEC adoption by state
Frequently Asked Questions
Which NEC edition do these calculators use?
The NEC-table calculators reference the NEC 2023 edition (NFPA 70-2023), and each names the table or section it used. The bending tools are pure geometry and cite their bender profiles instead, not a code edition. Check your local jurisdiction for adopted edition, since some areas still enforce the 2020 or 2017 NEC.
Can I use these calculators for permit applications?
These calculators are educational tools that help you verify your work. Always confirm calculations against the NEC code book and consult with your local AHJ (Authority Having Jurisdiction) for permit requirements.
Why do wire size results enforce the 75°C column?
Per NEC 110.14(C), conductor ampacity is limited by the terminal temperature rating of connected equipment, typically 75°C for most breakers and devices. Even with 90°C-rated wire like THHN, the final ampacity cannot exceed the 75°C column value. The 90°C rating is only used as the starting point for derating calculations.
Running the business side too?
The code math is only half the job. Check your hourly rate against real overhead numbers, or clear up markup vs margin before your next bid.