What does a BMI of 17.7 mean at 5'9"?
According to the WHO/NHS standard BMI classification, a Body Mass Index of 17.7 is in the Underweight band. At a height of 5'9" (about 175 cm), the official healthy weight range is 56.8–76.5 kg (125.2–168.7 lbs, or roughly 8 st 13 lb to 12 st 1 lb).
A weight of 120 lbs (54.4 kg) is 2.4 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.