If youre wanting a min 8mm fillet you will probably end up with 10mm. A 10mm fillet will weigh about 0.5Kg per metre length.
If you maintain 8mm perfectly it will only be 0.35 Kg/m
Now depending on your wire diamter, the amps and the man with the torch in his hand you could deposit anything up to 5Kg / hour. Assuming 1 Kg hour, you will weld between 2 and 3 metres.