Ideal weight

I just been onto a website to see what my ideal weight is. I'm 5ft and weighing 121lbs (roughly 8 1/2 stone). It said that people of my height should be about 108lbs thats like 7 1/2 stone I think. My body mass is 23.6. Grrr lol. I can't go lower than what I am really cause you got to be over 7 st 12 to give blood. Silly websites

For goodness sakes!

It's so blimming annoying isn't it!