Ahem cough cough splutter...
Okay then my friends.
Let's go with BMI (not that airline...) but Body Mass Index. It is rough indication of how over or underweight you are. It is not ideal because people can genuinely be bigboned etc etc.. but it's not bad.
Yo calculate your BMI do the following sum:
Body weight in KG / height in metres squared
ie: 75 kg / (1.75 x 1.75)
A normal person with no problem will crop up at a value of 25. Under 20 suggests malnourishment and over 30 is where the term obesity begins... but do not worry. 'Obese' in this phraseology means overweight, not that you are a Mr Stay Puft. So 20 to 30 is okay!
If you get to BMI 50 though... I'd cut down on cream cakes.
Any more help required drop me a line,
Flying Doc