I have designed data centers and computer-based offices many times over the decades. I am a Google architect. For years the trend line was lower power consumption each year. However, with the current trend of more CPU power and power-hungry GPUs, that trend is no longer as true. As AI and ML...
The simplest method is to read the power consumed on the UPS display. If you do not have a UPS, get one. Otherwise buy an inexpensive power usage meter.
I use a rule of thumb for modern (2020+) desktop computers. Typical i5/i7, two monitors: 250W or 900 BTUs. Now add another 50-100W or 170-340...