What BMI is — and isn't
BMI (Body Mass Index) is a simple screening tool that relates weight to height. It's widely used because it's easy to compute and correlates, at a population level, with body-fat percentage.
BMI = weight (kg) / height (m)² BMI = weight (lb) / height (in)² × 703
BMI does not measure body fat directly and does not distinguish between muscle and fat. Athletes with high muscle mass often have a BMI in the "overweight" category despite low body fat. Conversely, someone with low muscle mass can have a "normal" BMI while carrying unhealthy amounts of fat.
Use BMI as one data point alongside waist circumference, body composition measurement, and medical judgement — not as a standalone health verdict. This calculator gives an estimate for information only and is not medical advice.
How to calculate BMI by hand
Metric example: 72 kg and 175 cm tall.
- Convert height to meters: 175 cm = 1.75 m.
- Square it: 1.75 × 1.75 = 3.0625.
- Divide weight by that number: 72 ÷ 3.0625 = 23.5.
Imperial example: 158 lb and 5 ft 9 in tall.
- Convert height to inches: 5 × 12 + 9 = 69 in.
- Square it: 69 × 69 = 4,761.
- Divide weight by that number and multiply by 703: 158 ÷ 4,761 × 703 = 23.3.
Both results fall in the normal weight range. For 5 ft 9 in, that range is about 125.3 to 168.6 lb.
Categories (WHO)
- Underweight: below 18.5
- Normal weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obese: 30 and above
These adult cutoffs are the same for men and women and do not change with age. Some guidance, such as the UK's NICE, uses lower thresholds for people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background: 23 for increased risk and 27.5 for high risk.
BMI weight ranges by height
| Height | Normal (18.5–24.9) | Overweight (25–29.9) | Obese (30+) |
|---|---|---|---|
| 5 ft 0 in | 94.7–127.5 lb | 128.0–153.1 lb | 153.6 lb and up |
| 5 ft 3 in | 104.4–140.6 lb | 141.1–168.8 lb | 169.4 lb and up |
| 5 ft 6 in | 114.6–154.3 lb | 154.9–185.3 lb | 185.9 lb and up |
| 5 ft 9 in | 125.3–168.6 lb | 169.3–202.5 lb | 203.2 lb and up |
| 6 ft 0 in | 136.4–183.6 lb | 184.4–220.5 lb | 221.2 lb and up |
| 6 ft 3 in | 148.0–199.2 lb | 200.0–239.2 lb | 240.0 lb and up |
| Height | Normal (18.5–24.9) | Overweight (25–29.9) | Obese (30+) |
|---|---|---|---|
| 155 cm | 44.4–59.8 kg | 60.1–71.8 kg | 72.1 kg and up |
| 160 cm | 47.4–63.7 kg | 64.0–76.5 kg | 76.8 kg and up |
| 165 cm | 50.4–67.8 kg | 68.1–81.4 kg | 81.7 kg and up |
| 170 cm | 53.5–72.0 kg | 72.3–86.4 kg | 86.7 kg and up |
| 175 cm | 56.7–76.3 kg | 76.6–91.6 kg | 91.9 kg and up |
| 180 cm | 59.9–80.7 kg | 81.0–96.9 kg | 97.2 kg and up |
| 185 cm | 63.3–85.2 kg | 85.6–102.3 kg | 102.7 kg and up |
| 190 cm | 66.8–89.9 kg | 90.3–107.9 kg | 108.3 kg and up |
Getting an accurate reading
- Measure height without shoes, standing straight against a wall. An inch of error can move BMI by more than half a point.
- Weigh yourself at a consistent time, ideally in the morning before eating, since weight can swing a few pounds during the day.
- Track the trend, not one number. A change in BMI over months tells you more than any single reading.