It depends how much of that 1000W you are using. In and of itself with nothing hooked up to it my inverter draws less than an amp.
After that, wattage=volts X amps.......
So, if you plug in a 60 watt light bulb it will draw 60/12=5A.......
Once again I have installed one of these:
http://www.jamestowndistributors.com...ems+AC+Ammeter
They are VERY easy to install and it allows you to manage your AC load, which keeps you from overloading your inverter, or genny.
I also have a battery condition monitor, which tells me what the draw, or charge on my batteries is. These are a little harder to install but now I have complete vital signs on my electrics.
And, with them I have proven that the above formula is actually correct.....