Girls, do you give Ibuprofen strictly by weight? We used to have Nuofe…

Girls, do you give Ibuprofen strictly by weight? We used to have Nuofen Forte. I always calculated by weight. Now we bought Ibuprofen, but the dosage is such that if by weight, you need to give whole 9 ml. And in the instructions, weight 17-20 kg - 7.5 ml, not more than 450 mg per day.