How to use the BMI Calculator
- Choose units (metric cm/kg or imperial ft/in/lb) and enter height and weight.
- Pick the cut-offs: WHO international, WHO Asian or Chinese adult standard.
- Read your BMI, category and healthy weight range; optionally add age, sex and activity to estimate BMR and TDEE.
- Under 18, use paediatric growth charts instead of adult categories.
How BMI is calculated
BMI = weight (kg) ÷ height (m) squared. For 170 cm and 65 kg: 65 ÷ 1.7² ≈ 22.5. In imperial units, BMI = 703 × pounds ÷ inches squared. BMI Prime is BMI divided by the upper normal limit (25 for WHO, 24 for China); below 1 means within the normal limit.
Three sets of cut-offs
WHO international: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese. Chinese adult standard (WS/T 428-2013): under 18.5 underweight, 18.5–23.9 normal, 24–27.9 overweight, 28 and above obese. A 2004 WHO expert consultation suggested 23 and 27.5 as public-health action points for Asian populations, who tend to carry more body fat at the same BMI.
Limits of BMI, and BMR/TDEE
BMI does not separate muscle from fat, so athletes may score high and older or less muscular people low; waist circumference adds useful information. BMR is estimated with the Mifflin-St Jeor equation and TDEE = BMR × an activity factor; both are population-average estimates. Pregnant people, children and anyone with a chronic condition should follow medical advice.
Frequently asked questions
What is a normal BMI?
Under WHO international cut-offs, 18.5–24.9 is normal. Under the Chinese adult standard, 18.5–23.9 is normal.
Can children use this calculator?
It computes the number, but ages 2–18 must be assessed with age- and sex-specific growth percentiles, so the tool hides adult categories under 18.
Does a normal BMI mean I am healthy?
Not necessarily. BMI only reflects weight relative to height; waist size, body fat, blood pressure, blood sugar, lipids and lifestyle matter too.
How accurate is BMR?
Mifflin-St Jeor is one of the most widely used equations, but individual variation can exceed ±10%, so treat it as a starting point for planning.
Is my data saved?
No. Everything is calculated on your device, never uploaded and cleared when you refresh.