Body mass index is a quick screening measure used worldwide to compare weight with height. It is cheap and easy, but it does not measure body fat directly.
How to use it
Enter your weight and height in any unit; switching units keeps your value. Type a target BMI into the result to see the weight that would give it.
Adult BMI categories
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 and above: obesity
Limitations
BMI can overestimate fat in muscular people and underestimate it in older adults. Some populations, including many South Asian groups, face higher health risk at lower BMI values. Children and teens need age- and sex-specific percentiles instead. Combine BMI with waist measurement and a clinician’s advice.
Inputs explained
| Field | What to enter |
|---|---|
| Weight | Units: kg, lb, st, g |
| Height | Units: cm, m, in, ft |
What each result means
- Body mass index = [Weight] ÷ ([Height]÷100)^2
- Healthy weight from = 18.5 × ([Height]÷100)^2
- Healthy weight to = 24.9 × ([Height]÷100)^2
Example values
How the main result changes when Weight changes and everything else stays at the example values above:
| Weight (kg) | Body mass index (kg/m²) |
|---|---|
| 35 | 11.4 |
| 52.5 | 17.1 |
| 70 | 22.9 |
| 87.5 | 28.6 |
| 105 | 34.3 |
| 140 | 45.7 |
Formula
BMI = weight (kg) ÷ height (m)²Worked example
Weight 70 kg, height 175 cm (1.75 m).
BMI = 70 ÷ 1.75² = 70 ÷ 3.0625 ≈ 22.9, healthy weight.
Healthy range for 1.75 m: 18.5 × 3.0625 ≈ 56.7 kg to 24.9 × 3.0625 ≈ 76.3 kg.
Key terms
- BMI
- Body mass index, weight divided by height squared, in kg/m².
- Healthy weight range
- Weights that give a BMI from 18.5 to 24.9 at a given height.
- Waist circumference
- A complementary measure of abdominal fat linked to health risk.
Frequently asked questions
Is BMI accurate for athletes?
Not always. Muscle is dense, so muscular people can have a high BMI with low body fat.
Does BMI differ for men and women?
The adult formula and categories are the same for both sexes.
Can children use this calculator?
No. Under 20 years, BMI must be compared with growth charts for age and sex.
What is a healthy BMI?
For most adults, 18.5 to 24.9.
What formula does the BMI Calculator use?
BMI = weight (kg) ÷ height (m)².
Can I work backwards from the result?
Yes. Type the result you want into Body mass index and the calculator finds the matching weight.