Not sure if your weight is in the healthy range? Our free UK BMI calculator uses NHS guidelines and accepts your measurements in stones and pounds or kilograms — whichever you prefer.
👉 Calculate your BMI free on Kalkulo
What Is BMI?
Body Mass Index (BMI) is a simple calculation using your weight and height to estimate whether you're a healthy weight. The NHS uses BMI as an initial screening tool to identify adults who may be underweight, overweight, or obese.
How to Calculate BMI in the UK
The standard metric formula:
BMI = Weight (kg) ÷ Height² (m)
Prefer stones and feet? Convert first:
- 1 stone = 6.35 kg
- 1 foot = 0.3048 m
For example, someone weighing 11 stone (69.9 kg) at 5'9" (1.75 m): BMI = 69.9 ÷ (1.75 × 1.75) = 69.9 ÷ 3.0625 = 22.8
Save yourself the hassle — use our free BMI Calculator which handles all conversions automatically.
NHS BMI Categories for Adults
| BMI | Weight Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight ✅ |
| 25.0 – 29.9 | Overweight |
| 30.0 – 39.9 | Obese |
| 40.0 and above | Severely obese |
Healthy Weight Ranges by Height (Stones & Pounds)
| Height | Healthy Weight | Overweight Starts At |
|---|---|---|
| 5'2" | 7st 11 – 10st 6 | 10st 7 |
| 5'5" | 8st 6 – 11st 4 | 11st 5 |
| 5'8" | 9st 2 – 12st 4 | 12st 5 |
| 5'11" | 9st 13 – 13st 4 | 13st 5 |
| 6'1" | 10st 9 – 14st 4 | 14st 5 |
BMI and Ethnicity: NHS Guidance
The NHS recommends lower BMI thresholds for people from South Asian, Chinese, and Black African or Caribbean backgrounds, as research shows these groups face higher health risks at lower BMI levels: