Electrical Calculators

Most electrical conversions come down to three relationships. Ohm's law ties voltage, current and resistance together as V = I × R. Power is voltage times current, so W = V × A. And energy is power times time, which is where watt-hours and kilowatt-hours come from. Nearly every calculator in this category is one of those three rearranged, and each page shows which one it is using.

The complication is power factor. In an AC circuit, apparent power (VA or kVA) is what the supply has to deliver, while real power (W or kW) is what actually does work — and the ratio between them is the power factor. That is why kVA and kW are different numbers for the same load, and why a generator or UPS is rated in kVA rather than watts. A purely resistive load like a heater has a power factor of 1 and the two figures match; motors and switching supplies do not.

Phase matters too. A three-phase conversion carries a factor of √3 (about 1.732) that a single-phase one does not, so using the wrong mode gives an answer that is off by roughly 73 percent — a large enough error to size a cable wrongly. Every calculator here that depends on phase asks for it rather than assuming, and battery-focused tools like amp-hours to watt-hours ask for the pack voltage, since capacity in Ah means nothing without it.