Kalkulo

BMI calculator

Work out your body mass index in stones and pounds and read your NHS category, with lower thresholds for South Asian, Chinese and Black adults.

Result
22.9
Normal
152540

About this tool

Why use this tool

Body Mass Index (BMI) is used by the NHS, NICE and Public Health England as a quick screening for weight-related health risks. It helps flag whether your weight sits in a healthy range for your height and indicates increased risk of type 2 diabetes, coronary heart disease and stroke — conditions the NHS treats as major public health priorities.

How the calculation works

The metric formula is BMI = weight (kg) ÷ height (m)². In stones and pounds: convert to kg (1 stone = 6.35 kg) then apply the formula. NHS categories for adults: under 18.5 = underweight, 18.5–24.9 = healthy weight, 25.0–29.9 = overweight, 30.0–39.9 = obese, 40+ = severely obese. For people of Asian, Chinese, Middle Eastern, Black African or African-Caribbean family background, NICE lowers the overweight threshold to 23 and obese to 27.5.

Real example

A person 1.75 m tall (5'9") weighing 12 stone (76.2 kg) has a BMI of 76.2 ÷ (1.75 × 1.75) = 24.9. They sit at the top of the healthy range according to NHS guidance. At 13 stone (82.6 kg) the BMI rises to 27.0, moving into the overweight category.

Practical tips

BMI does not measure body fat distribution. Combine it with waist circumference (raised risk above 80 cm for women and 94 cm for men according to NHS). Follow the Eatwell Guide, aim for 150 minutes of moderate activity a week and 5-a-day fruit and vegetables. Speak to your GP for a free NHS Health Check (available every 5 years from age 40 to 74) or a referral to a registered dietitian via the HCPC register.

Disclaimer

This calculator gives an indication only and is not a medical diagnosis. It is not suitable for children (use NHS growth charts), pregnant women, competitive athletes or people over 65. Always consult your GP or NHS 111 for personalised advice.

Frequently asked questions

How does the NHS use BMI?⌄
The NHS uses BMI as a first-line screening tool to assess weight-related health risk in adults. A BMI of 18.5 to 24.9 is classed as healthy, 25 to 29.9 as overweight, and 30 or above as obese. GPs use BMI alongside waist measurement, blood pressure, and blood tests before recommending weight management services or referral to NHS Digital Weight Management programmes.
Are BMI thresholds different for Black, Asian and minority ethnic groups in the UK?⌄
Yes. NICE guidance recommends lower BMI thresholds for people of South Asian, Chinese, Black African and African-Caribbean backgrounds, because they face increased cardiometabolic risk at lower body weights. For these groups, overweight starts at a BMI of 23 and obesity at 27.5. This adjusted threshold is used by the NHS when assessing type 2 diabetes and heart disease risk.
Can I use stones and pounds with this BMI calculator?⌄
Yes — the UK version of our calculator accepts stones and pounds as well as kilograms, and feet and inches as well as centimetres. BMI itself is always computed in metric (kg divided by height in metres squared), but the conversion happens automatically. This means you can enter 12 st 4 lb and 5 ft 9 in and get an accurate result without doing any conversion yourself.
Does BMI work for children in the UK?⌄
Adult BMI categories do not apply to children and teenagers. The NHS uses BMI centile charts that compare a child's BMI with others of the same age and sex, based on UK growth reference data. A child above the 91st centile is considered overweight and above the 98th centile very overweight. The National Child Measurement Programme uses this approach in Reception and Year 6.
What does the NHS recommend if my BMI is over 30?⌄
If your BMI is 30 or above, the NHS recommends speaking to your GP about a structured weight management plan. This may include referral to a free NHS weight management service, dietary support, and physical activity guidance of at least 150 minutes of moderate exercise per week. For BMI over 35 with related conditions, medication or bariatric surgery may be considered under NICE criteria.

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