BMI Calculator UK
Units
Waist measurement (optional)
Measure halfway between your lowest rib and the top of your hip bone.
Enter your height and weight,
then tap Calculate BMI.
BMI Calculator UK – Check Your BMI in Stones and Pounds
This free BMI calculator for the UK works in stones and pounds, feet and inches or in kilograms and centimetres, and uses the same adult BMI categories as the NHS. It tells you your Body Mass Index, whether you are underweight, a healthy weight, overweight or obese, and the healthy weight range for your height in stones and pounds. It also applies the lower BMI thresholds recommended by NICE for people from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds, and can check your waist-to-height ratio.
How to Use the BMI Calculator
- Choose stones and feet, or kg and cm.
- Enter your height and weight. Weigh yourself in light clothing, without shoes, ideally at the same time of day.
- Select your ethnic background so the correct thresholds are used.
- Optional: enter your waist measurement to see your waist-to-height ratio.
- Tap "Calculate BMI".
BMI Categories Used by the NHS
| BMI | Category | For South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds |
|---|---|---|
| Below 18.5 | Underweight | Below 18.5 – underweight |
| 18.5 – 24.9 | Healthy weight | 18.5 – 22.9 – healthy weight |
| 25 – 29.9 | Overweight | 23 – 27.4 – overweight |
| 30 – 39.9 | Obese | 27.5 and above – obese |
| 40 and above | Severely obese |
NICE recommends lower thresholds for people from these ethnic backgrounds because they have a higher risk of type 2 diabetes, heart disease and stroke at a lower BMI.
BMI Formula
BMI = weight (kg) ÷ height (m)²
In imperial units: BMI = weight (lb) × 703 ÷ height (in)². One stone = 14 lb = 6.35 kg, and one inch = 2.54 cm. For example, someone who is 5 ft 9 in (1.753 m) and weighs 11 st (69.9 kg) has a BMI of 69.9 ÷ 1.753² = 22.7 – a healthy weight.
Healthy Weight Chart (Stones and Pounds)
| Height | Healthy weight (BMI 18.5 – 24.9) |
|---|---|
| 5 ft 0 in | 6 st 11 lb – 9 st 1 lb |
| 5 ft 3 in | 7 st 6 lb – 10 st 1 lb |
| 5 ft 6 in | 8 st 3 lb – 11 st 0 lb |
| 5 ft 9 in | 8 st 13 lb – 12 st 1 lb |
| 6 ft 0 in | 9 st 10 lb – 13 st 2 lb |
| 6 ft 3 in | 10 st 8 lb – 14 st 3 lb |
Waist-to-Height Ratio
NICE also recommends measuring your waist, because fat around the middle is linked to a higher health risk even at a healthy BMI. Divide your waist by your height (in the same units):
- Below 0.5 – no increased health risk. Keep your waist to less than half your height.
- 0.5 to 0.59 – increased health risk.
- 0.6 or more – high health risk.
Limitations of BMI
- BMI does not tell the difference between muscle and fat, so muscular people may be classed as overweight.
- It does not show where fat is stored – waist size adds important information.
- It is not suitable during pregnancy.
- For children and teenagers aged 2 to 18, BMI is compared with age and sex-specific growth centiles instead of adult categories.
- Older adults may benefit from slightly different targets – discuss with your GP.
What to Do Next
If your BMI is in the overweight or obese range, even losing 5% of your body weight can lower blood pressure, blood sugar and cholesterol. The NHS offers a free 12-week weight loss plan app, and your GP can refer you to local weight management services. If your BMI is below 18.5, talk to your GP to rule out underlying causes and get advice on healthy weight gain.
Frequently Asked Questions
What is a healthy BMI in the UK?
For most adults a healthy BMI is 18.5 to 24.9. For people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds, the healthy range is 18.5 to 22.9.
How do I calculate BMI in stones and pounds?
Convert stones to pounds (× 14), add the pounds, multiply by 703 and divide by your height in inches squared. The calculator does this automatically.
What BMI is classed as obese?
30 or above for most adults, and 27.5 or above for people from the ethnic backgrounds with lower thresholds. A BMI of 40 or more is severely obese.
What is the ideal weight for 5 ft 6 in?
A healthy BMI of 18.5 to 24.9 at 5 ft 6 in corresponds to roughly 8 st 3 lb to 11 st 0 lb (52 to 70 kg).
Is BMI accurate for athletes?
Not always. Muscle weighs more than fat, so athletes can have a high BMI without excess fat. Waist-to-height ratio gives extra context.
Is my data saved?
No. The calculation happens in your browser and nothing is stored.
Sources: NHS – BMI calculator and healthy weight guidance; NICE guideline NG246 / CG189 (overweight and obesity management, including ethnicity-specific BMI thresholds and waist-to-height ratio).