Is low fat measured by per 100 gram or the food unit as a whole?

I ask as I always used to look at the fat content in what I am eating for the whole food (say a tin of soup would be 9.6 fat per pot or 2.2 per 100g) so i dont think 9.6 ( i was told 5% or less is considered low fat) is particularly low fat but if its based on per 100g would it be? Could you eat this and lose weight? Would appreciate answers from an expert in diet & nutrition.