Before selecting a step down transformer, first we need to determine the rating of your equipment. This will normally be marked on the back of the unit, near the power cord, or in the instruction manual. It will be given as Amps (A) or Watts (W).
Now, just multiply the Amps by the voltage, ie. 110V x 10A = 1100VA (This is the most reliable method)
However, sometimes only the Watts are given, in this case we divide Watts by 0.85, ie. 800W / 0.85 = 941VA
Now we have the equipment rating in VA, select a transformer slightly larger. ie. if your equipment is 1100VA, then you will need the 1650VA transformer.
Keep in mind, you can also run multiple pieces of equipment from one transformer. Just add all the VA's together to get your total VA requirement for the transformer. Then, use a USA multi-socket power board plugged into the transformer.
Three phase transformers are calculated differently, please see our three phase transformers page.