Calculate your adult body mass index using metric or imperial measurements, see your NHS-based category and estimate a healthy weight range for your height.
Enter your measurements
Choose the second option if you are from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background.
Your result
Your BMI result and healthy weight range will appear here.
Muscular adults may have a high BMI without having excess body fat. Discuss concerns with a healthcare professional.
How the BMI calculator works
BMI compares your weight with the square of your height. In metric units, the formula is weight in kilograms ÷ height in metres². Imperial entries are converted to kilograms and metres before the same formula is applied. The result is rounded to one decimal place.
This tool follows NHS adult guidance. BMI cannot distinguish muscle from fat and should be considered alongside other health information.
Adult BMI categories
| Category | Standard threshold | Lower risk threshold |
|---|---|---|
| Underweight | Below 18.5 | Below 18.5 |
| Healthy weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25.0 to 29.9 | 23.0 to 27.4 |
| Obese | 30.0 or above | 27.5 or above |
The NHS advises lower overweight and obesity thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds because health risks can occur at a lower BMI.
Worked example
An adult weighing 70 kg and measuring 170 cm has a BMI of 24.2 (70 ÷ 1.70²). Using standard thresholds, that is in the healthy range. The estimated healthy weight range is approximately 53.5 kg to 72.0 kg.
What your result means
BMI is useful as a quick population-level screening tool, but it is not a direct measurement of body fat. Age, muscle mass, health conditions and ethnic background can affect how the number should be interpreted. Seek professional advice if your result worries you or if your weight is changing unexpectedly.
If you are pregnant, do not use adult BMI to assess pregnancy weight. You may instead find our Pregnancy Due Date Calculator useful for estimating dates, while clinical advice should come from your midwife or doctor.
Sources and methodology
Guidance checked for the 2026/27 tax year publication cycle. BMI guidance is health guidance and is not tax-year dependent.
Frequently asked questions
What is a healthy BMI for most adults?
For most adults, the standard healthy BMI range is 18.5 to 24.9.
Why are there lower thresholds for some ethnic backgrounds?
The NHS notes that the risk of health problems can increase at a lower BMI for certain ethnic groups, so overweight starts at 23 and obesity at 27.5.
Can I use this calculator during pregnancy?
No. Adult BMI is not suitable during pregnancy. Ask your midwife or doctor for appropriate guidance.
Does BMI measure body fat?
No. BMI uses height and weight, so it cannot distinguish muscle from fat or show where fat is carried.
Can children use this calculator?
No. Anyone under 18 needs an age- and sex-specific child BMI assessment.