Anyone working with power tools professionally should seriously consider working with 110 Volts. It is normally required, under Health and Safety regulations, when working on site, to use only 110 Volt tools. If a tool is to be used for only between 15-30 minutes at a time then the transformer rating needs only to match the tool rating. However, if you propose to use the tool for longer periods then choose a transformer with a slightly higher continuous rating. Where two tools are to be used simultaneously then add the wattage of the tools together before choosing the transformer. For example, a 2,000W 9" grinder used for 20 minutes would require an 2,250VA transformer but if the same tool was used for a longer period it would require an 3,300VA transformer on which a 500W drill could be used at the same time. The only other piece of advice worth giving is - buy the biggest you can afford, you never know what tomorrow might bring.
Model 102174, Tool Rating - 3,300VA,
Continuous Rating - 1,650VA, Outlet - 2 x 16A