It would depend on your height. Use the BMI calculator below.
I would suggest that you give your height as well, that way we can find out your BMI (Body Mass Index). Without this, it's not possible.
I think every BMI under 18, 5 is considered underweight.
you are a healthy weight! check your BMI http://www.nhlbisupport.com/bmi/ to know for sure.
go to this page, bmi is a much more reliable science: http://www.nhlbisupport.com/bmi/
If you've calculated your BMI you should have seen the recommended span as well, so I don't know if this is a serious question. 11.5 is a dangerously low BMI and you could well stand to gain 40 pounds or so.
17-19
Actually, your BMI is probably 18.5, which is normal: http://www.nhlbisupport.com/bmi/bmicalc.htm and http://www.whathealth.com/bmi/formula.html A low BMI could also just mean that you have low amounts of muscle. Muscle weighs more than fat so it can affect BMI calculations
A BMI Number Between 19 and 25 Is Considered Normal. To Get Your BMI Number Take You Weight In Kilograms Divided By Your Height In Meters Squares KG/M squared.
According to BMI, Body Mass Index, a 25-year old's weight should be about 51 kg to 56 kg.A way to calculate your BMI is weight (in kg)/height*height(in metres)eg: 40kg/1.5m*1.5m=40kg/2.25m=17.78 (approx)Normal BMI for a growing child is 17 to 24.9Normal BMI for an adult is 18.5 to 24.9You can also check your BMI at the following site: http://www.nhlbisupport.com/BMI/bmi-m.htm
15/17 Male-Female Sex 15/17 Male-Male Sex 15/17 Female-Female Sex
In my area its about 18.6, 19. But if your below about 17 then your underweight. But if you have been the way you are your whole life and you have a bmi of like 17 then your healthy. bmi standers dont work that well. I was 17.8 and i was perfectly healthy
The Normal Weight based on BMI is 104-140 lbs.