Hi my weight is 43 kgs and i aim for a weight of around 50 kgs.how much ensure drink should i take per day and for how many months?

Why not gaining lbs?: A rule of thumb--to gain 1 pound eat 3000 calories more than your body normally burns. A bigger question is why are you having difficulty gaining weight? Have you explored with your doctor the possibility of undernutrition, hyperthyroidism, malabsorption and maldigestion, infection, altered GI tract function, eating disorders, inflammatory conditions, and malignancy? Pursue evaluation please.