Category · Electrical
Electrical Calculators — NEC 2023 (Conduit Fill, Wire Size, Voltage Drop)
Free NEC 2023 electrical calculators for conduit fill, conductor sizing and ampacity, and voltage drop — three tools that chain together from raceway planning to final breaker selection.
Conduit Fill
Fill %, jam ratio, min size. Live now.
Wire Size
Ampacity per 310.16 with derating. Live now.
Voltage Drop
3% / 5% checks, min size, max distance. Live now.
NEC 2023 guide
Electrical calculators that chain together
These three NEC calculators follow the order electricians actually work: prove the wires fit, prove they carry the load, prove the volts arrive. The conduit fill calculator checks EMT, PVC, RMC, IMC, flex, and ENT raceway fill against NEC Chapter 9 Table 1 — 53% for one wire, 31% for two, 40% for three or more, 60% for short nipples — with jam-ratio warnings and auto-sized ground conductors per Table 250.122. The wire size and ampacity calculator sizes copper and aluminum conductors per Table 310.16, applying temperature correction, 310.15(C)(1) bundling derating, 110.14(C) terminal caps, and 240.4(D) breaker limits. The voltage drop calculator checks the 3% branch / 5% total guidance across DC, single-phase, and three-phase runs, with K-method speed and Table 9 Advanced accuracy for motors and steel conduit.
The electrical code calculator workflow
A feeder or branch circuit is one chain of decisions, and each electrical code calculator here handles one link. First, list every conductor — hots, neutral, ground — and run conduit fill: the count sets the Table 1 percentage and the ground counts toward area. Second, size the wire: start derating at the insulation column, apply ambient and bundling factors, cap at the terminal column, respect small-conductor breaker limits, and add the 125% continuous-load factor for EV chargers and heaters. Third, check voltage drop for the actual one-way distance: #12 copper that passes ampacity at 20A still fails 3% past about 60 ft on 120V. When any link fails, the tool names the fix — bigger conduit, bigger wire, shorter run.
NEC tables behind the numbers
Every result cites its table so the answer survives inspection. Conduit fill uses Chapter 9 Table 1 limits, Table 4 raceway areas, and Tables 5/8 conductor areas. Ampacity uses Table 310.16 with Table 310.15(B)(1) temperature correction and Table 310.15(C)(1) bundling adjustment, capped by 110.14(C) terminals and 240.4(D) small-conductor rules. Voltage drop uses Table 8 K-factors and circular mils for Basic mode, plus Table 9 R/X with power factor and conduit type for Advanced mode. Ground sizing follows Table 250.122 everywhere. For raw values, open the conduit NEC tables, wire ampacity tables, and voltage drop NEC tables.
When each tool governs the answer
Short branch circuits in cool, uncrowded raceways are usually ampacity jobs: Table 310.16 plus terminal limits decide. Packed conduits with 4+ current-carrying conductors become derating jobs: 310.15(C)(1) can remove 20–50% of table ampacity before temperature even applies. Long runs become voltage-drop jobs: drop scales with distance while ampacity does not, so feeders, detached garages, and 12V solar runs fail drop first. Tight raceways with mixed sizes become fill jobs where jam ratio and the 40% limit decide the trade size. Run all three checks on any real circuit — passing one never proves the others.
Guides
Go deeper
Conduit Fill Chart
How many THHN wires fit in 1/2, 3/4, 1″ EMT & PVC.
Wire Size Chart
What size for 20A, 30A, 50A, 100A, 200A — Cu + Al.
Max Distance Chart
How far 12, 10, 8 AWG run at 3% — feeders, EV, solar.
How to Calculate Conduit Fill
Worked examples: mixed sizes, ground, jam ratio.
How to Size Wire
Attic derating, EV charger, subpanel walkthroughs.
How to Calculate Voltage Drop
Kitchen, EV, 480V feeder, 12V solar examples.
Copper vs Aluminum
Size equivalents, drop parity, cost break-even.
FAQ
Electrical calculator questions, answered
Which electrical calculator should I use first?
Start with conduit fill to prove the wires fit, then wire size for ampacity and breaker selection, then voltage drop for long runs. Each tool links to the next in the chain.
Does the ground wire count in these calculators?
The ground counts toward conduit fill per Chapter 9 Note 3, and the wire-size tool auto-sizes it per Table 250.122. Grounds never count as current-carrying for derating.
When does bundling derating apply?
More than three current-carrying conductors in one raceway triggers Table 310.15(C)(1): 4–6 ×0.80, 7–9 ×0.70, 10–20 ×0.50. The wire-size calculator applies it automatically.
Do I size for continuous loads differently?
Yes — loads running 3+ hours need conductors at 125% of load current per 210.19(A)(1). EV chargers, heaters, and lighting are typically continuous.
What changed from 2020 to 2023 NEC code?
GFCI protection expanded to all 125V dwelling receptacles, surge protection required for dwellings (230.67), Table 310.16 reorganized with new 310.12, neutral load revisions, and reconditioned equipment rules. All calculators here follow NEC 2023.
Where can I find a NEC load calculation worksheet?
NEC Article 220 covers standard and optional dwelling methods, with worked examples in Annex D. For the conductor side, enter your VA load, voltage, and phase in the wire-size tool above.
What is the NEC 125% rule?
Continuous loads running 3+ hours need conductors and overcurrent protection at 125% of load current per 210.19(A)(1), 215.2(A)(1), and 230.42. A 40A continuous load needs a 50A conductor and breaker basis.
What are the basic electrical calculations?
Ohm's law (V=I·R), power (P=V·I), fill % (wire area ÷ conduit area), ampacity (Table 310.16 plus derating), and voltage drop (2·K·I·L÷CM). All five run on this page's tools.
What is an electrical calculator?
A tool that applies NEC tables to your inputs — conduit areas, ampacity columns, K-factors — and returns a code-cited answer instantly instead of manual table lookups.
What are the types of electrical calculations?
By purpose: conductor sizing, raceway fill, voltage drop, load calculation (Article 220), fault-current, and grounding. This page covers the first three end to end.
What are the types of electrical calculators here?
Conduit fill checks space, wire size checks current capacity, voltage drop checks volts delivered. Chain them: fill first, then size, then drop.
Which tool is used for calculation?
Match the job: pulling wire through raceway uses conduit fill; picking AWG and breaker uses wire size; checking a long run uses voltage drop. Start with the tool grid at the top of this page.