BMI calculator
BMI calculator.
Work out your body mass index in metric or imperial units. Your measurements stay on this page — they aren’t saved, sent anywhere or used for analytics.
What BMI is
Body mass index (BMI) compares your weight with your height: your weight in kilograms divided by your height in metres, squared. It’s a quick, general measure used for adults aged 18 and over.
General adult BMI ranges
The NHS uses these general ranges for most adults:
- Below 18.5 — underweight range
- 18.5 to 24.9 — healthy weight range
- 25 to 29.9 — overweight range
- 30 or above — obesity range
Ethnicity and BMI
People from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds have a higher risk of some health conditions at a lower BMI. UK guidance therefore uses lower thresholds for these groups — for example, 23 instead of 25 for the overweight range, and 27.5 instead of 30 for the obesity range.
What BMI can’t tell you
BMI is a screening measure, not a diagnosis. It doesn’t distinguish between muscle and fat, or show where weight is carried. It isn’t used in the same way for children, during pregnancy, or for some older adults and very muscular people.
Healthcare professionals often look at waist measurement too: a waist measurement of more than half your height can indicate increased health risk.
What to do with your result
Your result is general information. It doesn’t mean you need — or are suitable for — any particular treatment. If you’re worried about your weight or health, speak to your GP or another qualified healthcare professional. For practical ideas, read our guide to weight management.
Frequently asked questions
Is this BMI calculator suitable for children?
No. It’s for adults aged 18 and over. Children’s BMI is assessed differently, using age- and sex-specific centiles.
Can I use stone and pounds?
Yes. Switch to imperial to enter your height in feet and inches and your weight in stone and pounds.
Does my BMI mean I qualify for treatment?
No. BMI is only one general measure. Whether any treatment is appropriate is a clinical decision made by a qualified healthcare professional who considers your health as a whole.
Are my measurements stored?
No. The calculation happens in your browser. Your height and weight aren’t saved, sent anywhere or used for analytics.
Sources and further reading
This page is for general education only. It isn’t medical advice, it doesn’t recommend any treatment, and it doesn’t replace a conversation with a qualified healthcare professional about your own circumstances. If you need urgent medical help, call 999 or NHS 111.