How BMI is calculated
Body mass index (BMI) estimates whether your weight is in a healthy range for your height:
BMI = weight (kg) ÷ height (m)²
BMI = 703 × weight (lb) ÷ height (in)²
For example, at 5 ft 9 in (69 inches) and 160 lb: 703 × 160 ÷ 69² = 23.6, which is a healthy weight. The calculator uses exact unit conversions, so its results match the metric formula.
Healthy weight by height
With the WHO categories, a healthy weight is a BMI from 18.5 to under 25:
| Height | Healthy weight |
|---|---|
| 5 ft 0 in | 94.7 to 128 lb |
| 5 ft 4 in | 107.8 to 145.6 lb |
| 5 ft 8 in | 121.7 to 164.4 lb |
| 6 ft 0 in | 136.4 to 184.3 lb |
Different cut-offs in some countries
At the same BMI, many Asian populations have more body fat and a higher risk of diabetes and heart disease. Some countries therefore use lower cut-offs. Taiwan, for example, counts a BMI of 24 or more as overweight and 27 or more as obese. This page uses the WHO international categories.
Frequently asked questions
Is BMI accurate?
BMI only uses height and weight, so it can’t tell muscle from fat. Very muscular people can have a high BMI without much body fat, and older adults can have a normal BMI with more fat than it suggests. It doesn’t apply during pregnancy. Treat it as a first check, alongside waist size or body fat.
Can I use this for children?
No. For children and teens, BMI is compared with growth charts for their age and sex (BMI-for-age percentiles). These adult categories only apply from age 18.
Is a normal BMI enough?
Not always. Fat around the waist carries more health risk, so a large waist is worth checking even with a normal BMI. These results are for information only; talk to a doctor if you have concerns about your weight.