About ElectricalToolbox

ElectricalToolbox is a free hub of calculators, lookup tools, and reference charts for licensed electricians, electrical engineers, contractors, apprentices, and inspectors. The tools cover the calculations that come up on the job (voltage drop, conductor sizing and ampacity derating, conduit fill), with the National Electrical Code method behind each one stated plainly on the page.

How the tools are built

Every calculator's method and constants are derived directly from the published NEC tables: Chapter 9 Tables 1, 5, 8, and 9, Table 310.16 and its correction tables, and the applicable article for each topic. The page states which NEC edition it references (2020 by default). Each tool is backed by a suite of hand-derived reference scenarios checked against the source table, and results are cross-checked against independent industry calculators as a sanity check. Where this site's assumptions deliberately differ from another tool's (for example, defaulting to unity power factor as the conservative choice), the methodology section on the page says so.

Who runs it

The site is built and maintained by Jared Hebb. It exists because most online electrical calculators don't show their method, don't state their NEC edition, and quietly bake in assumptions you can't see, which makes them hard to trust for real work. This site's rule is the opposite: the table, the formula, and the assumptions are on every page, and the calculator is free with no sign-up.

A note on scope

Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance. Corrections and suggestions are welcome; see the contact page.