Hi Precious, No, I think you'd have to have a scale to know how much you weigh. If you have a measuring tape, you could measure your bust/waist/hips/thighs and that would probably paint a more accurate picture.
I know that muscle weighs more than fat, so it is possible that if you weigh yourself on a scale and you are mostly muscle and no fat, the number would be larger than your body would look like. And by the same token, if you are blubbery fat, you might weigh less in numbers than what you would look like.
The fact that you said you wanted to be half the size you are now told me you must know what you weigh now, but I guess you don't. Anyway, for talking purposes, lets say you now weigh 100 lbs, at 5'10" you would not be healthy and you would not look good AND you surely wouldn't want to be weighing 50 lbs....
So, let's say you weigh 200 lbs right now today. At 5'10" tall you probably look really good, but if you diet and exercise 1/2 of that body mass away...you would be 100 lbs and look and feel awful and most likely be close to death.
My father was 5'9" tall and weighed 120 lbs and he looked terribly ill. A woman with his same frame would look very very slim. Do you want to weigh 150 at your height? Would that be 1/2 your weight do you think?
I need to know either your weight or your measurements before I can guide you or give you advice on a way for you to lose that will not kill or deform you. NJoy