BMI Calculator
Calculate your Body Mass Index in metric, US or UK units, with US CDC or UK NHS adult categories.
Enter your height and weight
CDC adult categories are the same for everyone aged 20 and older, regardless of sex or race. For ages 2 through 19, CDC uses BMI-for-age percentiles instead. Children and teens: our Child & Teen BMI Calculator (CDC percentiles) or the CDC Child and Teen BMI Calculator. Ranges from CDC: Adult BMI Categories. BMI is a screening measure, not a diagnosis.
How to Use the BMI Calculator
- 1Choose the category system: CDC (US) or NHS (UK). They share the main cut-offs but name and group the categories differently.
- 2Pick your units: metric (cm, kg), US (feet, inches, pounds) or UK (feet, inches, stone and pounds).
- 3Enter your height and weight. In NHS mode you can also tick the family-background option, which applies the NHS's lower thresholds.
- 4Select Calculate BMI to see your BMI, your category and where it sits on the scale.
- 5Check the healthy weight range for your height, shown in the units you entered.
Frequently Asked Questions
What is BMI and how is it calculated?
Body Mass Index (BMI) compares your weight with your height: weight in kilograms divided by height in metres squared. With pounds and inches, the usual shortcut is weight (lb) × 703 ÷ height (in)². This calculator converts every unit to kilograms and metres first, using the exact definitions 1 lb = 0.45359237 kg and 1 in = 2.54 cm.
What are the BMI categories?
For adults aged 20 and over, the CDC uses Underweight (less than 18.5), Healthy Weight (18.5 to less than 25), Overweight (25 to less than 30) and three obesity classes from 30. For adults aged 18 and over, the NHS uses underweight (under 18.5), healthy weight (18.5 to 24.9), overweight (25 to 29.9) and obese (30 or more).
Is a high BMI always bad?
Not necessarily. BMI cannot tell the difference between muscle and fat, so people with a lot of muscle can have a high BMI with little body fat. It is a screening measure, not a diagnosis — talk to a doctor about your weight and health.
Why does the NHS mode ask about family background?
The NHS says people from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background are at risk of health problems at a slightly lower BMI, so it treats 23 to 27.4 as overweight and 27.5 or higher as obese for them. The option is off by default and only changes the NHS categories.
Can I use this calculator for children?
No. Adult categories apply from age 20 (CDC) or 18 (NHS). Children and teenagers are assessed with BMI-for-age percentiles, which depend on age and sex — use the CDC or NHS child calculator linked under the calculator.
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NHS BMI Categories 2026 — Complete Guide to UK Weight Classifications
Full guide to NHS BMI categories 2026. Covers all weight ranges, the lower thresholds for some family backgrounds, and a built-in BMI calculator.
🇺🇸CDC BMI Categories for Adults (with Calculator)
Check your CDC BMI category with the built-in calculator, then see the full adult chart, the three obesity classes and when BMI can be misleading.
⚖️Healthy BMI for Women — NHS Ranges, Charts & What They Mean (2026)
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⚖️Understanding BMI: UK (NHS) vs US (CDC) Guidelines 2026
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