QUICK: Divide watts by 10.
- For example, your 240V appliance shows a rating of 300W.
 - 300 / 10 = 30A
 - This appliance will draw 30A from your 12V batteries when running through an inverter.
 
DETAIL:
- Watts are Watts and remain the same whether running from 240VAC or 12VDC through an inverter.
 - Inverter efficiency is approximately 85%
 - Watts = Volts x Amps
 - So, a 300W appliance, running on 12v:
300W / 12V / 85% = 29.4A