Electrical: Calculators & Wiring Guides
1 calculator
Electrical is the trade where a remodel project most often crosses from "I can measure this myself" into "I need to understand this before I talk to anyone." Finishing a basement means new circuits. Converting a garage means a subpanel feed. Adding a hot tub, a well pump, or a workshop at the far end of the yard means a long wire run — and long runs are where wiring plans quietly go wrong, because the wire that is perfectly rated for the load can still starve it of voltage over distance. The calculators in this hub exist for exactly that planning moment: they put real numbers on your circuit before you buy wire or call an electrician, so you can sanity-check a plan or a quote instead of nodding along.
The first tool in the hub is the voltage drop calculator — the long-run workhorse. Enter your circuit, wire gauge, load, and one-way distance and it returns the drop in volts and percent, the voltage your equipment actually receives, and the longest run each gauge supports within the commonly cited 3% recommendation. It is also honest about what that 3% figure is: an Informational Note recommendation in the NEC, not enforceable code — a distinction this hub takes seriously everywhere.
Every electrical tool here follows the same rules: the math comes from published NEC tables with the edition named, results are sizing references only, and every output carries the same advice — electrical work almost always needs a permit and inspection, many states limit what homeowners may legally do themselves, and a licensed electrician and your local Authority Having Jurisdiction have the final word. Wire size, breaker sizing, and project-specific tools for hot tubs, mini-splits, and subpanel feeds are on the roadmap for this hub. Free, no signup.
Electrical calculators
Frequently Asked Questions
What is voltage drop and why does it matter?
Voltage drop is the voltage lost as current pushes through the resistance of the wire itself — the longer and thinner the wire, the more you lose. It matters most on long runs to wells, detached garages, sheds, and hot tubs, and it matters most for motors: a pump starved of voltage draws more current, runs hotter, and fails earlier. The voltage drop calculator computes the loss for your exact circuit and run.
Is the 3% voltage drop limit an actual code requirement?
No. The widely quoted 3% branch-circuit and 5% combined figures come from Informational Notes to NEC 210.19 and 215.2(A), and NEC 90.5(C) states Informational Notes are explanatory, not enforceable. They remain good engineering practice — excessive drop wastes energy and shortens motor life — but in most jurisdictions an inspector cannot fail an installation on voltage drop alone. A few local codes do adopt hard limits, so always check yours.
Can homeowners legally do their own electrical work?
It varies by state and local jurisdiction. Many states let an owner-occupant pull a permit and wire their own single-family home with required inspections — Washington, Minnesota, and Michigan have explicit homeowner provisions. Others are restrictive: Massachusetts largely requires licensed electricians, New York City requires a licensed master electrician, and Hawaii generally requires a contractor even for homeowners. Rentals and multifamily buildings are excluded nearly everywhere. Confirm with your local Authority Having Jurisdiction before planning any work.
What size wire do I need for my circuit?
Two separate checks decide it: the conductor must carry the load safely (ampacity, per NEC Table 310.16 with its correction factors and the breaker rules of 240.4(D)), and it must deliver acceptable voltage over the distance (the voltage drop calculator handles that side). On short runs ampacity governs; past roughly 75–100 feet, voltage drop usually forces the wire a size or two larger than ampacity alone would require. A dedicated wire-size tool for this hub is in the works — until then, verify conductor choices with a licensed electrician.
Which edition of the NEC applies to my project?
Whichever edition your state or local jurisdiction has adopted — typically the 2020 or 2023 NEC as of 2026, with adoption lagging publication by two to four years. The core math on this hub (the K-factor voltage-drop method from Chapter 9 Tables 8–9) is unchanged across editions, but table numbering and some requirements differ between editions, so any code citation should name the edition. Your local Authority Having Jurisdiction can tell you which edition is enforced where you live.