Electronics is the category where the definitions do the work. An ohm is defined so that one volt across it drives one ampere, and a watt so that one volt at one ampere delivers a joule every second — so every formula here is those two statements rearranged, not an empirical rule with exceptions. What the arithmetic will not tell you is where it stops applying: a diode is not a resistor, an inductor on alternating current is not either, and a part rated exactly at the power it dissipates is a part running too hot. Each tool says where its own limits are.
Give any two of voltage, current, resistance and power, and this works out the other two — including the power the resistor has to dissipate, which is the figure that decides whether it survives.
Work out what two resistors in series do to a supply voltage, how much current they draw doing it, and how much each of them turns into heat.
Work out the series resistor an LED needs on a given supply, rounded up to a value you can actually buy, with the power it has to dissipate.
Tell us what is missing and where its numbers should come from.
What should it convert, calculate or generate, and where would the authoritative numbers come from? A link to the standard or publication that defines them is the most useful thing you can send.
Opens your mail app with this page already filled in.
Every tool in this category runs entirely in your browser: there is no upload, no account and no request to a server once the page has loaded. The numbers behind them are transcribed from the organisation that defines them — NIST for units, the W3C for web formats, the WHO for health measures — and each page names its source next to the formula. A tool whose reference values stop reproducing fails the build and does not ship, which is the whole reason the catalogue grows slowly.