How is BMI calculated?
The formula is BMI = weight (kg) / height² (m²). Someone 175 cm tall weighing 70 kg has a BMI of 70 / (1.75 × 1.75) = 22.9, which is in the healthy range. In US units: BMI = 703 × weight (lb) / height² (in²). BMI applies to adults over 18 and uses the same cut-offs for men and women.
BMI chart: the WHO categories
| Category | BMI |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5-24.9 |
| Overweight | 25.0-29.9 |
| Obesity, class I | 30.0-34.9 |
| Obesity, class II | 35.0-39.9 |
| Obesity, class III | 40.0 and above |
Healthy weight for your height
A healthy weight is usually defined as the range where BMI sits between 18.5 and 24.9. It is a range, not one number: at 170 cm anything from 53.5 to 72 kg counts as healthy. Where you feel best inside it depends on your muscle, frame and training.
| Height | Healthy weight |
|---|---|
| 150 cm | 41.6-56 kg |
| 155 cm | 44.4-59.8 kg |
| 160 cm | 47.4-63.7 kg |
| 165 cm | 50.4-67.8 kg |
| 170 cm | 53.5-72 kg |
| 175 cm | 56.7-76.3 kg |
| 180 cm | 59.9-80.7 kg |
| 185 cm | 63.3-85.2 kg |
| 190 cm | 66.8-89.9 kg |
| 195 cm | 70.3-94.7 kg |
When BMI gets it wrong
BMI cannot tell what your weight is made of. A muscular lifter can have a BMI of 26-27 with low body fat, while someone who rarely exercises can have a normal BMI and a high body fat percentage. In older adults, loss of muscle can make BMI underestimate fat.
- Athletes and anyone with a lot of muscle: BMI overestimates fat. Check your body fat percentage too.
- Waist size shows where fat sits; fat around the middle matters more for health.
- Children and teenagers are assessed on age- and sex-specific BMI percentiles, so this calculator is not for under-18s.
- BMI is not used to judge weight during pregnancy.
What to do with your result
If you want to lose fat, the calorie calculator shows how much to eat each day and the protein calculator how much protein helps you keep muscle while you do. If your BMI is below the healthy range or your weight is changing without you trying, talk to a doctor.
Frequently asked questions
What is a healthy BMI?
For adults, the WHO classes a BMI of 18.5 to 24.9 as healthy. 25 to 29.9 is overweight, 30 and above is obesity and below 18.5 is underweight.
How do I calculate my BMI?
Divide your weight in kilograms by your height in metres squared. At 175 cm and 70 kg: 70 / (1.75 × 1.75) = 22.9. In pounds and inches, multiply weight by 703 and divide by height in inches squared.
What is a healthy weight for 170 cm (5 ft 7 in)?
At 170 cm, the healthy BMI range of 18.5-24.9 is 53.5 to 72 kg (about 118 to 159 lb).
Is BMI accurate for athletes?
Not always. BMI does not separate muscle from fat, so it can overestimate fat in muscular people. Body fat percentage and waist size are more useful there.
Can children use this BMI calculator?
No. Under 18, BMI is judged on age- and sex-specific percentile charts; ask your child’s doctor.