BMI calculator
Calculate body mass index from your height and weight, see which WHO category it falls into and the healthy weight range for your height.
Adult WHO thresholds. Not medical advice; BMI does not measure body fat directly.
How this calculator works
BMI is a single number that relates weight to height: weight in kilograms divided by height in metres squared, or 703 × weight in pounds divided by height in inches squared. It was designed as a quick population-level screening tool, not a diagnosis. For most adults it correlates well enough with body fat to flag risk, which is why doctors, insurers and public health bodies still use it.
It has real limitations. BMI cannot tell muscle from fat, so a trained athlete can be classified overweight. It says nothing about where fat sits, and visceral fat around the organs matters more than total weight. It also uses fixed thresholds that are applied differently for children, and Asian populations are advised to use lower cut-offs because cardiometabolic risk rises at a lower BMI. Use the category as a prompt for a conversation, not a verdict.
The formula
Metric: BMI = weight (kg) ÷ height (m)². US customary: BMI = 703 × weight (lb) ÷ height (in)². The healthy range is BMI 18.5–24.9, so the weight range for a given height is BMI × height²:
BMI = kg / m²
healthy weight low = 18.5 × height²
healthy weight high = 24.9 × height²Categories: under 18.5 underweight, 18.5–24.9 normal, 25.0–29.9 overweight, 30 and above obese (WHO adult thresholds).
Worked example
At 180 lb and 5 ft 10 in, the BMI is 25.8, which is in the Overweight range. For that height, a BMI between 18.5 and 24.9 corresponds to roughly 129–174 lb.
Common mistakes
- Using BMI to judge athletes. Muscle is denser than fat, so heavily muscled people often score in the overweight range while carrying little fat.
- Ignoring waist circumference. Waist size and waist-to-height ratio add information about visceral fat that BMI cannot see.
- Applying adult thresholds to children. Children and teenagers are assessed on age- and sex-specific percentile charts, not the adult cut-offs.
Frequently asked questions
What is a healthy BMI?
For most adults the WHO defines 18.5–24.9 as the healthy range. Some guidelines suggest lower upper limits for people of Asian descent because risk rises at a lower BMI.
Does BMI measure body fat?
Not directly. BMI is a proxy based on weight and height. Body-fat scales, calipers and the US Navy tape method give a better body-fat estimate; DEXA scans are the reference method.
Is BMI accurate for everyone?
No. It is least reliable for very muscular people, older adults who have lost muscle, pregnant women and children. It is a screening tool, not a diagnosis.
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