Dear Anik - the simplest answer is to measure rather than calculate the power consumption. A simple device such as the Adafruit mini power meter

https://www.adafruit.com/product/3624

will allow you to monitor the power consumption in operation. If you are power a raspberriy pi over usb then any of the usb power meters at amazon will do the job - the slightly more expensive ones will even output a graph to your phone of power consumption over time!

Another option is to use an oscilloscope or multimeter with data logging capabilities if they are available to you. This can be done by measuring the current drawn from your entire system (using a shunt resistor) along with the voltage of your power supply. It is usually wise to measure the voltage instead of just assuming it will remain at its expected value.

Once you have this data you can derive whatever units you need. The power consumption of wireless nodes are often reported as time-averaged current (see most wireless microcontroller datasheets). You can also observe the current draw in different states of operation by looking at current consumption over time. You can get your power by multiplying corresponding current and voltage datapoints. If you want energy, you can do a time integral of your power data.

There are many options but the simplest one is using of power meters in a simulated environment (of course with real RPi). Also, you can use a simple DC current meter (which is available with less than 5$) and feed the information through a GPIO and log the information with the RPi. As the input voltage is fixed you can calculate the power impact during the test period.

Thank you very much for your suggestions.

Dear Anik Islam Abhi ,

you can mainly distinguish the measure of (i) power consumption from the (ii) energy calculation. The (i) is easy to determine (as already suggested by collegues) and its measurement can confirm (or not) what is already known in literature (for the same work point and subjecting the system to the same stresses). The (ii) point, instead, should be "splitted" in several subpoint depending from the IoT scenario, use of computational resources, software running on board, etc. Try to write and execute a script that automatically monitor your board. Furthermore you can graph results in the observation/monitoring time period through a "smart" environment (e.g., Grafana https://grafana.com/grafana with InfluxDB).

Dear Maurizio Giacobbe ,

Thanks for your suggestion. I will give a try.