The only real way of knowing is to measure it. If you already have a system in place an energy monitoring smart plug can help you calculate the current running

The only real way of knowing is to measure it. If you already have a system in place an energy monitoring smart plug can help you calculate the current running costs and help estimate the savings of using a lower-power machine. When I did this I was surprised by how much - or how little - it cost to run various devices. It's quite addictive. It's not always accurate because a lower-power machine doing the same task will often need to work at its full power more often, so the savings may be less. For example, a Raspberry Pi 5 may often be more power effecient than a Pi 4, despite drawing more power at full capacity on paper, because it spends less time at full capacity than the Pi 4 does. On the other hand, when I upgraded my work PC I found it used less power but I also had to run my office heater more often in winter, as the new PC wasn't as efficient at heating the space.