Calculating wattage requirement for 12v invertor

[The Sultan]

I am travelling around aust with the family and rather than by car chargers for all of our laptops, cameras, DS's etc decided to buy a 12v to 240v invertor.

I know the formula is Amps x Volts = Wattage, but just need a hand to read the labels on my stuff so i know which size inverter to puchcase.

for eg. the charger on my laptop states
Input: AC100-240v, 50-60hz, 1.5A.

am i right to assume that is equates to 100 x 1.5 = 150 watts.

most of the chargers are around this figures so would I only need a 300-600w inverter to charge my bits???

 

[Jafa]

These guys will know. FWIW I would try for a pure sine wave if it's within your budget.