Power factor in a single-phase circuit can be measured with the wattmeter-ammeter-voltmeter method, where the power in watts is divided by the product of measured voltage and current.

You can measure the phase-shift between voltage and current by means of an oscilloscope or analyzer. The power factor is cos(x) of this angle.

See,

Power factor is basically cosine diffrent between voltage waveform and current waveform.

In order to measure power factor we have three methods

1.standard pf meter

2.you can have Current waveform by using ct and voltage waveform using potential transformer.. then you need to convert the sinusoidal waves into square wave.then xor will give you millisecond diffrence between i.e you can calculate pf very easily and accurately.

3.using module known as pzem-004t.

Using this module you can have voltage, current, frequency, powerfactor very easily and accurately...

My research paper is based on this..will upload soon

With a single-phase, two-wire system , the voltage and current detected by the wattmeter are equal to the total power dissipated by the load. The voltage is measured between the two wires, and the current is measured in the wire supplying power to the load, often called the hot wire

https://www.yokogawa.com/library/resources/media-publications/how-to-measure-electrical-power/

http://docshare01.docshare.tips/files/693/6938988.pdf

https://stacyhome.ru/en/elektroizmeritelnye-pribory/measurement-of-power-in-singlephase-ac-circuits-electrical-measurements-in-threephase-circuits/

The answer above all assume sinusoidal waveforms, which is seldom true at liter loads and smps. Harmonics may also affect the measurements.