What formula does this BMI calculator use?
BMI is weight in kilograms divided by height in metres squared. Imperial measurements are converted before the same calculation is applied.
BMI & Weight Range Calculator
Calculate adult BMI, compare interpretation thresholds, and understand a height-based weight interval.
Workspace
Adult BMI inputs
Enter height and weight
This calculator uses adult categories for people aged 20 or older. Children and teenagers require age- and sex-specific percentiles.
Category guide
Standard adult thresholds
Underweight< 18.5
Healthy weight18.5–<25
Overweight25–<30
Obesity (class 1)30–<35
Obesity (class 2)35–<40
Obesity (class 3)≥ 40
How to interpret this result
BMI is a general screening measure, not a diagnosis or direct measurement of body fat. It does not distinguish fat from muscle or bone and needs cautious interpretation for highly muscular adults, during pregnancy, for some health conditions, and in later life. Discuss health or weight concerns with a qualified healthcare professional.
Reference guidance: CDC adult BMI categories and NICE adult assessment guidance.
GuideHow to use
- Enter an adult height and weight in metric or imperial units; switching units converts the current measurements.
- Choose standard adult thresholds or the lower risk-action thresholds used in UK guidance for some ethnic backgrounds.
- Review the category band, height-specific weight interval, position relative to that interval, and converted measurements.
- Copy the plain-language summary or download the result as CSV.
HelpFrequently asked questions
Is the displayed weight range a personal target?
No. It is the weight interval corresponding to the selected BMI interpretation at the entered height: 18.5 through 24.9 for standard thresholds or 18.5 through 22.9 for the lower-threshold guide. Individual health cannot be determined from BMI alone.
What are the lower risk-action thresholds?
UK guidance uses lower overweight and obesity thresholds for adults from South Asian, Chinese, other Asian, Middle Eastern, Black African, or African–Caribbean backgrounds because cardiometabolic risk can occur at a lower BMI. Select that interpretation only when it is relevant.
Why might BMI be misleading?
BMI compares weight with height but cannot distinguish fat, muscle, or bone. It also needs cautious interpretation during pregnancy, in later life, for highly muscular adults, and when a health condition affects height or body composition.
Can this be used for children?
No. Children and teenagers require age- and sex-specific BMI percentiles from an appropriate clinical calculator.
Keep working
