The short answer
BMI (body mass index) is your weight in kilograms divided by your height in metres squared. For most adults, a BMI of 18.5 to 24.9 falls in the healthy weight range, 25 to 29.9 is overweight and 30 or more is obesity. Use the calculator above for your own result.
Formulas and sources are named on this page. How we calculate.
How this is calculated
BMI compares your weight with your height. It is a quick screening number, not a measurement of body fat or a diagnosis.
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Worked examples
Metric: a person 175 cm tall who weighs 70 kg. Height in metres is 1.75, and 1.75² = 3.0625. BMI = 70 ÷ 3.0625 = 22.9, which is inside the healthy weight range of 18.5 to 24.9.
Imperial: a person 5 ft 10 in (70 in) tall who weighs 180 lb. BMI = 703 × 180 ÷ 70² = 126,540 ÷ 4,900 = 25.8, which falls in the overweight range of 25.0 to 29.9.
Where the categories come from. The adult cut-offs of 18.5, 25 and 30 are the ones published by the CDC and used by the World Health Organization. We label your result using the BMI as displayed to one decimal place, so the number and the category always agree.
What BMI cannot tell you
- It does not measure body fat directly. The CDC notes that BMI does not distinguish between fat, muscle and bone.
- It does not show where fat is carried on the body or what type it is.
- On its own it is not a diagnosis. The CDC says an individual assessment also looks at things such as medical history, health behaviours, a physical exam and blood tests.
If you train with weights or have a lot of muscle, try the body fat percentage calculator as a second view.
The Asian-population option
A WHO expert consultation in 2004 reviewed evidence that people of Asian background can have a higher risk of type 2 diabetes and heart disease at a lower BMI. It kept the international cut-offs but proposed extra action points at 23, 27.5, 32.5 and 37.5. When you tick the option, this calculator uses 23 and 27.5 as category boundaries: healthy weight is 18.5 to 22.9, overweight is 23.0 to 27.4 and obesity starts at 27.5.
BMI categories for adults
Adult BMI categories (kg/m²)| Category | Standard (CDC / WHO) | Asian-population cut-offs |
|---|
| Underweight | Below 18.5 | Below 18.5 |
| Healthy weight | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight | 25.0 – 29.9 | 23.0 – 27.4 |
| Obesity, class 1 | 30.0 – 34.9 | 27.5 or higher |
| Obesity, class 2 | 35.0 – 39.9 |
| Obesity, class 3 | 40.0 or higher |
Categories apply to adults. For ages 2 to 19 the CDC compares BMI with growth charts by age and sex instead.
Healthy weight range by height
These ranges use the standard healthy BMI band of 18.5 to 24.9.
Healthy weight (BMI 18.5 to 24.9) for adults| Height | Healthy weight (kg) | Healthy weight (lb) |
|---|
| 150 cm (4 ft 11 in) | 41.6 – 56 kg | 92 – 124 lb |
| 155 cm (5 ft 1 in) | 44.4 – 59.8 kg | 98 – 132 lb |
| 160 cm (5 ft 3 in) | 47.4 – 63.7 kg | 104 – 141 lb |
| 165 cm (5 ft 5 in) | 50.4 – 67.8 kg | 111 – 149 lb |
| 170 cm (5 ft 7 in) | 53.5 – 72 kg | 118 – 159 lb |
| 175 cm (5 ft 9 in) | 56.7 – 76.3 kg | 125 – 168 lb |
| 180 cm (5 ft 11 in) | 59.9 – 80.7 kg | 132 – 178 lb |
| 185 cm (6 ft 1 in) | 63.3 – 85.2 kg | 140 – 188 lb |
| 190 cm (6 ft 3 in) | 66.8 – 89.9 kg | 147 – 198 lb |
| 195 cm (6 ft 5 in) | 70.3 – 94.7 kg | 155 – 209 lb |
Frequently asked questions
What is a healthy BMI for adults?
For adults the CDC and WHO define a healthy weight as a BMI from 18.5 to 24.9. If you use the Asian-population cut-offs it is 18.5 to 22.9. A BMI inside the range does not guarantee good health, and one outside it is not a diagnosis.
Is BMI accurate for athletes and very muscular people?
Not always. BMI cannot tell muscle from fat, so a muscular person can have a BMI in the overweight range with a low body fat percentage. A body fat estimate can give a fuller picture.
Is BMI different for men and women?
The adult formula and the category cut-offs are the same for men and women. Body fat percentage does differ between the sexes, so it needs a separate measure.
Can I use BMI for a child or teenager?
No. For ages 2 to 19 the CDC reads BMI as a percentile against growth charts for the child's age and sex. Use the CDC child and teen BMI calculator, or ask a paediatrician or nurse.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide the result by your height in inches squared. For 180 lb and 70 in that is 703 × 180 ÷ 4,900, which is 25.8.
What should I do if my BMI is outside the healthy range?
Treat it as a prompt to look at the bigger picture. A doctor or registered dietitian can consider your waist size, blood pressure, blood tests, family history and how you feel before suggesting anything.
Disclaimer and editorial note
For information only, not medical advice. This calculator gives general estimates from the numbers you enter. It cannot diagnose, treat or prevent any condition and does not replace advice from a doctor, midwife, registered dietitian or other qualified professional who knows your history.
Written and maintained by the HealthFitnessHQ editorial team. We name the source of every formula and category used, and we review each calculator when guidance changes. Read how we work in our editorial policy and methodology.