How many square meter in each kg GI duct 0.8 mm thickness ????

For duct sheet of thickness (zero point eight) mm , This is Gauge (twenty two) . 

For Gauge (twenty two)  , and assuming it is Galvanized Steel ,

the weight =1. LB/Ft2 (one point four zero six)

Which equals =6. Kg/m2  (six point eighty six)

The answer of your question is

=1/6. m2/Kg =0. m2/Kg (zero point one forty six)