What AmpCalcs is
AmpCalcs is a set of free electrical and electronics calculators — voltage drop, conductor and wire sizing, conduit fill, box fill, service and kVA load, power factor, transformer sizing, Ohm's law, resistor colour codes and battery runtime. Ten tools in total. Each one answers a question you would otherwise work out by hand or look up in a code book, and each shows the formula and the working rather than only the final number.
Why it exists
Most electrical calculators online hand you a black box: one number and no way to check it. Every AmpCalcs result names the formula it used and, where one applies, the code article it follows, then shows the intermediate values — so you can follow the arithmetic and check it against the code book yourself. The site is free, needs no account, and runs entirely in your browser: nothing you type is uploaded.
Who maintains it
AmpCalcs is a small site built and maintained by an independent developer. It is not a company, an engineering firm or a licensed electrical contractor, and nothing here is a substitute for a qualified electrician or a stamped design. The calculators are reference tools: use them to understand a number and to check your own work.
How the calculators are kept honest
Where a recognised method applies, the formula follows the published reference — Chapter 9 tables for conduit fill, Article 314 for box fill, and the ampacity tables together with the voltage-drop equation for conductor sizing. Values that depend on your installation, such as conductor material, insulation temperature rating, terminations and run length, are inputs rather than hidden assumptions. Each page states what it assumes and what it does not cover.
Corrections and requests
If a calculator returns a result that does not match the code book, or a tool you need is missing, tell us through the feedback form at the bottom of any page. A useful report includes the inputs you entered, the result you got and the value you expected; leaving an email address is optional but lets us follow up.
Calculators and references last reviewed: 28 October 2026.