BMI Calculator

Work out your adult BMI in metric or imperial, see which NHS category it falls in and the healthy weight range for your height.

Reviewed by Dany, RightSums team · Updated

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health · Daily life · UK & US

Enter your height and weight in centimetres and kilograms, feet and inches, stone and pounds, or pounds only. The calculator divides your weight in kilograms by your height in metres squared and places the result in the NHS adult categories: below 18.5 underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight and 30 or more obese. Tick the box if you are from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background and it uses the NHS lower thresholds of 23 and 27.5. It also shows the healthy weight range for your height. It is for adults aged 18 and over only. BMI does not measure body fat and is not a diagnosis.

Accepted inputs

  • Age
  • Height in cm or feet and inches
  • Weight in kg, stone and pounds, or pounds
  • Ethnic background option

Outputs

  • BMI to one decimal place
  • NHS weight category
  • Healthy weight range for your height
  • Weight change to reach the healthy range

How to use the BMI Calculator

  1. Enter your age, then your height and weight in metric or imperial units.
  2. Tick the ethnic background box if it applies to you, as the NHS uses lower BMI thresholds for those groups.
  3. The calculator divides your weight in kilograms by your height in metres squared and rounds the answer to one decimal place.
  4. It then shows your NHS category and the weight range that would give you a healthy BMI at your height.

Frequently asked questions

How do I calculate my BMI?

Divide your weight in kilograms by your height in metres, then divide by your height again. Someone who is 170 cm tall and weighs 70 kg has a BMI of 70 ÷ (1.7 × 1.7) = 24.2. That falls in the NHS healthy range of 18.5 to 24.9.

What is a healthy BMI for adults?

The NHS puts a healthy BMI at 18.5 to 24.9 for most adults. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or more is obese. For someone 170 cm tall, a healthy BMI means weighing between about 53.5 kg and 72 kg.

Why is the BMI threshold lower for some ethnic groups?

The NHS says people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds face health risks at a lower BMI. For them, 23 to 27.4 counts as overweight and 27.5 or more as obese. So a BMI of 24.2 would be in the overweight range.

What is a healthy weight for 5ft 9in in stone?

At 5 ft 9 in, a BMI of 18.5 to 24.9 works out at roughly 8 st 13 lb to 12 st 1 lb. A person of that height who weighs 11 stone has a BMI of 22.7, which is in the NHS healthy range.

Can I use a BMI calculator for my child?

No. Adult BMI categories are for people aged 18 and over. The NHS has a separate BMI calculator for children and teenagers aged 2 to 17. If you enter an age under 18 here, you get a link to the NHS children's calculator instead of an adult result.

Sources

The rates and rules in this tool come from:

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