BMI calculator UK
Work out your body mass index in metric (kg and cm) or imperial (stone and pounds, feet and inches), then see what it means using NHS and NICE ranges.
Check your BMI
BMI (Body Mass Index) is a quick way to see how your weight compares with your height — a useful starting point, not a full picture of your health.
Your BMI
Enter your details and select Calculate.
BMI is a general guide and doesn’t account for muscle, body composition or other factors.
What is BMI?
Body mass index (BMI) is a way of using your height and weight to tell whether you’re a healthy weight for your height. It’s your weight in kilograms divided by your height in metres squared. For most adults, a BMI of 18.5 to 24.9 is in the healthy range. It’s a screening measure, not a diagnosis.
How BMI is worked out
BMI compares your weight with your height. It’s the same calculation whichever units you use.
Weight (kg) ÷ height (m)²
Divide your weight in kilograms by your height in metres, squared. Someone who weighs 70kg and is 1.70m tall has a BMI of about 24.2 (70 ÷ 1.70 ÷ 1.70).
703 × weight (lb) ÷ height (in)²
Convert stone to pounds (1 stone is 14lb) and feet to inches (1 foot is 12in), then multiply your weight by 703 and divide by your height in inches, squared. The calculator does the conversion for you.
Adult BMI ranges in the UK
For most adults, a healthy BMI is 18.5 to 24.9. The ranges are the same for men and women, but NICE sets lower thresholds for some ethnic groups.
| Category | Standard BMI | Lower thresholds* |
|---|---|---|
| Underweight | Below 18.5 | Below 18.5 |
| Healthy weight | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight | 25 – 29.9 | 23 – 27.4 |
| Obesity | 30 and above | 27.5 and above |
*For people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds. Sources: NICE NG246 and the NHS.
Why some thresholds are lower
People from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean family backgrounds tend to develop weight-related health risks, such as type 2 diabetes, at a lower BMI.
So NICE advises that, for these groups, overweight starts from a BMI of 23 and obesity from 27.5, rather than 25 and 30.
Adult BMI chart by height
Find your height, then read across. Each column shows the weight at which an adult’s BMI reaches that category, in stone and pounds and in kilograms.
| Height | Healthy weightfrom BMI 18.5 | Overweightfrom BMI 25 | Obesityfrom BMI 30 |
|---|---|---|---|
| 4ft 10in147cm | 6st 5lb40kg | 8st 8lb54kg | 10st 4lb65kg |
| 5ft 0in152cm | 6st 11lb43kg | 9st 2lb58kg | 11st 0lb70kg |
| 5ft 2in157cm | 7st 3lb46kg | 9st 11lb62kg | 11st 10lb74kg |
| 5ft 4in163cm | 7st 10lb50kg | 10st 6lb67kg | 12st 7lb80kg |
| 5ft 6in168cm | 8st 3lb53kg | 11st 1lb71kg | 13st 4lb85kg |
| 5ft 8in173cm | 8st 10lb56kg | 11st 11lb75kg | 14st 1lb90kg |
| 5ft 10in178cm | 9st 3lb59kg | 12st 6lb80kg | 14st 13lb95kg |
| 6ft 0in183cm | 9st 11lb62kg | 13st 2lb84kg | 15st 11lb101kg |
| 6ft 2in188cm | 10st 4lb66kg | 13st 13lb89kg | 16st 10lb106kg |
| 6ft 4in193cm | 10st 12lb69kg | 14st 9lb93kg | 17st 9lb112kg |
| 6ft 6in198cm | 11st 6lb73kg | 15st 6lb98kg | 18st 8lb118kg |
How to read the chart
- Below the healthy weight figure for your height is underweight (BMI under 18.5).
- Each weight is the lightest whole pound or kilogram at which BMI, to one decimal place, reaches that category. Centimetre heights are rounded, so the stone and kilogram figures can differ slightly.
- For people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds, NICE uses lower thresholds (23 and 27.5), so overweight and obesity start at lower weights than shown.
- For adults aged 18 and over. Not for children or during pregnancy.
For your exact figure, use the calculator above. Sources: NHS and NICE NG246.
The limits of BMI
BMI is a useful screening tool, not a diagnosis. It says nothing about where you carry weight, and it doesn’t suit everyone.
Muscle
BMI can’t tell muscle from fat, so very muscular people can get a high reading that overstates their risk.
Age
Readings should be interpreted with caution in people aged 65 and over.
Pregnancy
BMI isn’t used in the same way during pregnancy. Your midwife or GP will guide you.
Children
Under-18s are still growing, so their BMI is compared against growth-chart centiles for their age and sex, not the adult ranges.
Keep your waist to less than half your height
Fat carried around the middle carries the most health risk, and BMI can’t see it. So for adults with a BMI below 35, UK guidance says to measure your waist-to-height ratio too.
How to measure
- Find the point midway between the bottom of your ribs and the top of your hips.
- Wrap a tape measure around your waist at that point.
- Breathe out naturally, then read the tape.
- Divide your waist by your height, using the same units for both.
| Waist-to-height ratio | NICE category |
|---|---|
| 0.4 to 0.49 | Healthy central adiposity |
| 0.5 to 0.59 | Increased central adiposity |
| 0.6 or more | High central adiposity |
| Height | Keep waist under (0.5) |
|---|---|
| 5ft 0in (152cm) | 76cm / 30in |
| 5ft 4in (163cm) | 81cm / 32in |
| 5ft 8in (173cm) | 86cm / 34in |
| 6ft 0in (183cm) | 91cm / 36in |
Worked out from the 0.5 ratio, for guidance only. Sources: NICE NG246 and the NHS.
Talk to a GP about your weight — free consultation
If your BMI or waist-to-height ratio is higher than you’d like, our weight service starts with a free consultation with a GP: a proper conversation about your health and goals, and a plan built with you.
Free NHS support too
- See your GP, especially if you have a related condition such as high blood pressure or type 2 diabetes.
- The free NHS Weight Loss Plan app offers a 12-week plan.
- Adults aged 40 to 74 in England may be invited to a free NHS Health Check every five years.
Numbers aren’t the whole story. If you’re worried about your relationship with food or weight, please speak to a GP or contact Beat, the UK eating disorder charity.
Honest FAQs
Can I use this BMI calculator in stone and pounds?
Yes. Select Imperial and enter your height in feet and inches and your weight in stone and pounds. Select Metric to use centimetres and kilograms instead. Both give the same result.
What is a healthy BMI in the UK?
For most adults, a healthy BMI is 18.5 to 24.9. 25 to 29.9 is overweight and 30 or above is obesity. For people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds, NICE uses lower thresholds: overweight from 23 and obesity from 27.5.
Is BMI different for men and women?
No. The standard adult BMI ranges are the same for men and women, though they are lower for some ethnic groups.
Does age affect what a healthy BMI is?
Not for adults. The same BMI ranges apply to everyone aged 18 and over, although NICE advises interpreting BMI with caution in people aged 65 and over, taking other health conditions into account. Children and teenagers aged 2 to 17 are different: their BMI is compared with growth charts for their age and sex, so use the NHS BMI calculator for children instead.
Can I use this calculator for a child?
No. This calculator uses the adult ranges. Children and teenagers are still growing, so their BMI is compared with growth-chart centiles for their age and sex. The NHS has a separate BMI calculator for children.
What is a healthy waist size?
The simple rule is to keep your waist to less than half your height, which is a waist-to-height ratio below 0.5. Someone 5ft 8in (173cm) tall would aim for a waist under about 86cm (34in).
Is BMI accurate if I’m muscular?
Not always. BMI can’t tell muscle from fat, so it can overstate risk in very muscular people. Measuring your waist-to-height ratio as well gives a fuller picture.
Sources
The health information on this page is based on UK guidance:
Talk to a GP about your weight
Start with a free consultation — a proper conversation about your health and goals, not a checkout.