How to calculate BMI
- 1.
Choose units
Pick imperial (lb, ft, in) or metric (kg, cm).
- 2.
Enter height and weight
The result updates as you type - there is no button to press.
- 3.
Read the result
See your BMI, WHO category, its position on the scale, the healthy weight range for your height and how far you are from it.
BMI formula and worked example
Body mass index is weight divided by height squared: BMI = weight [kg] / (height [m])², or in imperial units BMI = 703 × weight [lb] / (height [in])².
Example: 5 ft 9 in (69 in) and 154 lb → 703 × 154 / 69² = 108,262 / 4,761 ≈ 22.7, which is normal weight. In metric: 70 kg at 175 cm → 70 / 1.75² ≈ 22.9.
To find the healthy range for any height, rearrange the formula: weight = BMI × height². At 1.75 m that is 18.5 × 3.0625 = 56.7 kg up to 24.9 × 3.0625 = 76.3 kg.
WHO BMI categories for adults
| BMI | Category |
|---|---|
| < 16.0 | Severe thinness |
| 16.0-16.9 | Moderate thinness |
| 17.0-18.4 | Mild thinness (underweight) |
| 18.5-24.9 | Normal weight |
| 25.0-29.9 | Overweight |
| 30.0-34.9 | Obesity class I |
| 35.0-39.9 | Obesity class II |
| ≥ 40 | Obesity class III |
The same cut-offs apply to adult men and women. Some health services use lower thresholds for people of Asian origin (e.g. overweight from 23), so check local guidance.
Healthy weight by height
| Height | Healthy weight (BMI 18.5-24.9) | Obesity from (BMI 30) |
|---|---|---|
| 5′ 0″ (152 cm) | 95-127 lb | 154 lb |
| 5′ 3″ (160 cm) | 104-141 lb | 169 lb |
| 5′ 6″ (168 cm) | 115-154 lb | 186 lb |
| 5′ 9″ (175 cm) | 125-169 lb | 203 lb |
| 6′ 0″ (183 cm) | 136-184 lb | 221 lb |
| 6′ 3″ (191 cm) | 148-199 lb | 240 lb |
The healthy range spans 30-50 lb because frames and muscle mass differ. Need to convert stones or kilograms first? Use the weight converter.
Limitations of BMI
BMI is a screening tool, not a diagnosis - it does not measure body fat. Very muscular people can score as overweight with little fat, while older adults may have a “normal” BMI despite low muscle mass. It is not used during pregnancy. A useful addition is waist circumference: according to the WHO, the risk of metabolic complications rises substantially above 88 cm (35 in) for women and 102 cm (40 in) for men.
Children and teens under 18 are assessed with BMI-for-age percentile charts for their sex; adult cut-offs do not apply and this calculator does not compute percentiles.
Frequently asked questions
What is a healthy BMI?
+
For adults, 18.5 to 24.9. 25-29.9 is overweight, 30 or more is obesity and below 18.5 is underweight.
How much should I weigh for my height?
+
The calculator shows the range matching BMI 18.5-24.9. For example, at 5 ft 9 in it is about 125-169 lb; at 170 cm about 53.5-72.0 kg.
Is BMI different for men and women?
+
No, the same WHO cut-offs apply to adult men and women. Waist size or body-fat measurements capture differences in body composition better.
Can I use this for children?
+
No. Children and teens are assessed with BMI-for-age percentile charts. Ask a paediatrician.
Is BMI accurate for athletes?
+
Often not. Muscle is denser than fat, so muscular people can have a BMI above 25 with a low body-fat percentage.
Is my data stored?
+
No. The calculation runs in your browser and nothing is sent or saved.
Updated: