Depending on what you are looking for, or trying to accomplish, you may, or may not need a formula per se.
For example, if all you need to know is how many volts, amps, watts, kva, or btu’s are used by a particular computer or other IT device for that matter, first things first check the “tag” or “label” on the device as well as included documentation, or, on-line spec sheets and documentation.
There are also some measuring devices including among others Kill A Watt that you can plug a device into and see volts, amps, watts, and so forth.
Ok, that might have been the obvious and easy part, now on to the next step.
Often a name plate may give kva however not watts, or perhaps amps and volts however not kva or some other metric. This is where the various conversion formulas come into play.
For example, if you know volts and amps, you can get watts, if you know kva along with watts, amps or volts, you can derive the others, or, if you have btus, you can watts, or if you know watts you can get btus and so forth.
Btu/Hour = watts * 3.413
Watts = Btu/Hour * 0.293
Watts = Amps * Volts
Volts = Watts / Amps
Amps = Watts / Volts
VoltAmps (Va) = Volts * amps
KVA = (Volts * Amps) / 1000
Here’s a link to some additional conversions and formulas that along with many others are found in my new book “The Green and Virtual Data Center”
In “The Green and Virtual Data Center” book, there is an entire chapter on metrics, where and how to find them, formulas, conversions as well as other related items including determining energy costs, carbon footprints, cooling and more across servers, storage, networks, facilities along with associated management tools.
Look for various sample chapter downloads via various TechTarget/IT Knowledge Exchange/BitPipe and related venues (look for promo codes to receive discounts on ordering the book.
Greg Schulz – Author of The Green and Virtual Data Center