BMI Calculator
Calculate body mass index in metric or imperial units.
Good to know. BMI can’t tell muscle from fat, so a rugby player can come out “overweight”. It’s a screen, not a verdict.
Not medical advice. A general estimate for healthy adults.
How it works
In plain words
Divide your weight in kilograms by your height in metres, squared. In imperial units, the same result comes from pounds ÷ inches² × 703.
The formula
BMI = weight (kg) ÷ height (m)² BMI = 703 × weight (lb) ÷ height (in)²
Worked example
70 kg at 1.75 m: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, which is in the healthy range.
Sources
- World Health Organization, Obesity and overweight The adult BMI categories.
Sources checked September 29, 2026. 6 automated tests check its answers on every change.
About the BMI calculator
Body mass index is a quick way to compare weight with height. It is widely used by doctors and health services because it is simple and needs no equipment, but it is a screening tool, not a diagnosis.
For adults, the World Health Organization uses these ranges: under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or more is obese. Some health services use lower thresholds for people of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean background, because health risks can rise at a lower BMI.
BMI has real limits. It can’t tell muscle from fat, so athletes and very muscular people can be classed as overweight while being perfectly healthy. It says nothing about where fat is stored, and fat around the waist carries more risk. It is also less reliable for older adults, and for pregnant people.
BMI for children and teenagers is calculated the same way but judged differently, using growth charts for age and sex. The adult categories here don’t apply to anyone under 18.
If your result worries you, talk to a doctor. Waist measurement, blood pressure and blood tests give a much fuller picture.
Questions people ask
What is a healthy BMI?
For most adults, 18.5 to 24.9. Some health services use lower cut-offs for certain ethnic backgrounds.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. 160 lb at 5 ft 9 in (69 in): 703 × 160 ÷ 4,761 = 23.6.
Is BMI accurate for athletes?
Not very. BMI can’t tell muscle from fat, so muscular people can get a high BMI while being healthy.
Can children use this calculator?
The formula is the same, but children’s results must be compared with growth charts for their age and sex. The adult categories don’t apply.