What does a BMI of 12.5 mean at 6'3"?
According to the WHO/NHS standard BMI classification, a Body Mass Index of 12.5 is in the Underweight band. At a height of 6'3" (about 191 cm), the official healthy weight range is 67.1–90.4 kg (147.9–199.3 lbs, or roughly 10 st 8 lb to 14 st 3 lb).
A weight of 100 lbs (45.4 kg) is 21.7 kg below the bottom of this healthy range.
A BMI in the underweight band may indicate undernutrition, an underlying medical issue, or insufficient calorie intake. A small calorie surplus, strength training, and a GP review can help. See our calorie calculator to find your daily target.
Key facts
- BMI is a screening tool, not a diagnosis. It works well for most adults but does not distinguish between muscle and fat.
- If you are very muscular or athletic, your BMI may overestimate body fat. Pair this result with a body fat percentage check.
- For South Asian, Chinese, or Black ethnic groups, NICE recommends lower thresholds (overweight at BMI 23, obese at BMI 27.5).
- For pregnancy, use our pregnancy BMI calculator with pre-pregnancy weight instead.
- For children and teens, use the child BMI calculator with age-and-sex percentile bands.