Use formula:
Power (watts) = Voltage (ac volts) times Current (amps)
Look for voltage and current ratings for each tool you will use and
multiply for power use of tool. With the tools you have or may have in the future, add the power of the combination of tools you may use on the generator at one time. This should give a minimum wattage generator you should get. If you are in the US the voltage is normally 120v ac, large appliances sometime require a higher voltage.
ie. Makita 9227 rotary is rated at 10amps. P=IxV , P=10 x 120= 1200 watts, so you would need a generator at with at least 1200 watts continuous power; now if you were to use another tool at the same time you would need a generator with enough wattage to run that tool also. ie. You may find that your extractor is rated 2200 watts now you need a generator at least
3400 watts.
Your other concern should be the surge wattage of generator for when you first start your tools. It will be a higher value than the continuous wattage.
This is how I figured what I needed. I hope I am not to late with the information.