- Under 18.5 — Underweight
- 18.5 – 24.9 — Healthy weight
- 25 – 29.9 — Overweight
- 30 – 34.9 — Obese
- 35+ — Severely obese
- BMI doesn't measure body fat directly
- Athletes may have high BMI due to muscle mass
- BMI may be less accurate for older adults
- Ethnicity can affect healthy BMI ranges
- Always consult a doctor for health advice
- Body Mass Index — weight divided by height squared
- Formula: kg ÷ m²
- Developed in the 1830s by Adolphe Quetelet
- Used by the NHS as a screening tool
How to use the BMI Calculator
Select your preferred units — metric (kg and cm) or imperial (stones, lbs, feet and inches). Enter your weight and height and your BMI is calculated instantly. See your category, healthy weight range for your height and how far you are from the ideal range.
Frequently Asked Questions
For most adults a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight. Between 25 and 29.9 is overweight. Between 30 and 34.9 is obese. 35 and above is severely obese. These are guidelines and individual health should be assessed by a doctor.
BMI has limitations. It does not distinguish between muscle and fat, so muscular athletes may have a high BMI without being unhealthy. It may also be less accurate for older adults who tend to have more body fat at a given BMI, and for different ethnic groups who may face health risks at lower BMI thresholds.
Our calculator shows the healthy weight range (BMI 18.5 to 24.9) for your specific height. This gives a personalised range rather than a single number, which is more useful for setting realistic goals.
BMI was developed in the 1830s by Belgian mathematician Adolphe Quetelet. It was designed as a population-level statistical tool and was never intended to be a diagnostic measure for individuals. Despite its limitations it remains widely used by the NHS as a quick screening tool.