It is the gap between the power an appliance actually uses and the current the supply has to deliver. Motors and some electronics draw more current than their wattage suggests, and an inverter rated in volt-amperes is describing that current rather than the useful power.
Power factor is the specification that explains why an inverter sized correctly in watts can still be undersized in practice.
Two different quantities
Real power is what does the work and what the meter bills. Apparent power is voltage multiplied by current, and it is what the supply, the cable and the inverter must actually handle. When they diverge, the equipment is sized on the larger one.
Where the divergence comes from
Loads that store and return energy each cycle — motors and transformers — draw current that does no net work. Some electronic supplies distort the current waveform instead, with a similar effect on the equipment upstream.
How it shows on a specification
A unit rated in volt-amperes is quoting apparent power. A unit rated in watts at a stated power factor is quoting both. The pair tells you what the inverter can supply to an awkward load, and it is the honest form of the specification.
Measuring rather than assuming
Energy meters that report power factor show it for a given appliance in a second. For a load list containing motors, that measurement is worth more than any category-based estimate, because the spread within a category is wide.
Where this page and the manufacturer’s documentation differ, the documentation is the one to follow. Every capacity, output, input window, current limit, cycle count and temperature threshold on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any peak figure: a surge rating means something only with the duration it can be held. A very short tolerance and a long one are printed identically. This page quotes the maker’s continuous rating as the figure to size against, reports a surge rating with its stated duration when one is published, and computes no starting current from either.
What people ask before they order
Why are some inverters rated in VA and others in watts?
Volt-amperes describe what the unit must supply; watts describe what a resistive load consumes. For loads with a poor power factor the two differ, and a unit quoting both is stating more than one quoting either alone.
Which appliances have a poor power factor?
Motors, transformers and some switch-mode supplies. A plug-in energy meter that reports power factor shows it directly, which is more reliable than assuming from the category.
Last reviewed 16 September 2026