How to Choose Transformers is an important area to consider when you begin the journey toward a transformer investment. How to Choose Transformers begins by determining the transformer’s capacity which is rated in volts-amps (VA). Operational voltage for most appliances and/or equipment should be visibly labeled as follows:
Current (Amps), Frequency (Hz), Voltage (Volts), Wattage (Watts or VA)

This voltage labeling is usually located on the back of the appliance. If labeled voltage cannot be located, it is fine to use the wattage in most cases. If the appliance labeling shows starting amps and running amps, it is best to use the running amps to calculate the wattage (VA).

How to Choose Transformers continues with the result of a basic Voltage x Amps calculation. With the resulting number, you now know How to Choose Transformers--with a VA rating equal to or larger than the VA listed on the appliance. It is always fine to use a transformer with a larger VA listing but using a transformer with a smaller VA rating could lead to overheating and/or burning out the transformer, which is not advisable.
In general, it is more cost effective to use one large transformer for several appliances than to have several transformers for each appliance. However, if you have an appliance that is frequently running (washing machine, freezer, etc.) and the transformer is permanently placed, that transformer should be left attached and dedicated solely to that one appliance.