What your BMI means
BMI is your weight in kilograms divided by your height in metres squared. Health bodies use it as a quick screening number for adults because it's easy to measure and, across large groups of people, it lines up with body fat and health risk.
| BMI | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| ≥ 30.0 | Obesity |
Waist-to-height ratio
Your waist says something BMI can't: how much fat you carry around your middle. NICE guidance in the UK suggests keeping your waist to less than half your height. Measure halfway between your lowest rib and the top of your hip bone, after breathing out normally.
The limits of BMI
BMI doesn't separate muscle from fat, so very muscular people can score as overweight. It also doesn't account for age or sex, and people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background have higher health risks at lower BMIs, which is why NICE uses lower thresholds (23 and 27.5) for these groups. It isn't meant for children, pregnant people or older adults without other measures.
Track your BMI over time
A single BMI is a snapshot. If you're changing your weight, the trend matters more than any one reading.
Frequently asked questions
What is a healthy BMI?
For most adults, the World Health Organization classes a BMI of 18.5 to 24.9 as a healthy weight. Lower thresholds are used for some ethnic groups.
Is BMI accurate?
It's a useful screening number for groups of people, but it can mislead for individuals, especially if you're very muscular, older, or from a group with different risk thresholds. Waist measurements add useful context.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. The calculator does this for you when you choose Imperial.
Does this calculator work for children?
No. Children and teenagers need age- and sex-specific BMI percentiles, which a doctor or a dedicated child BMI calculator can provide.
Sources
- World Health Organization: Obesity and overweight
- CDC: Adult BMI categories
- NICE NG246: Overweight and obesity management
- NHS: What is the body mass index (BMI)?
General information, not medical advice.