To define obesity WHO uses Body Mass Index. Many scientific Works showed that BMI is not enough to define obesity because 2 people which has same height and same weight may have different muscle mass ratios.
For now Body Mass Index method is the most favourite obesity measurement scale.
Body Mass Index: The weight of the person(kilograms) divided by height’s square(meters).for example height=1.73m and weight 110 kg 110/1.73×1.73= 36.8 => VKI