What does a BMI of 39.9 mean at 5'9"?
According to the WHO/NHS standard BMI classification, a Body Mass Index of 39.9 is in the Obese Class II 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 270 lbs (122.5 kg) is 46.0 kg above the top of the healthy range.
A BMI above the healthy range increases the risk of cardiometabolic conditions over time. Small, sustainable changes work best: a 500-kcal daily deficit (around 0.5 kg lost per week), 150 minutes of moderate activity, and improved sleep. See our calorie calculator and reverse BMI calculator to set a target weight.
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.