Advanced BMI Calculator
Calculate BMI with WHO classifications, ideal weight range, and BMI Prime.
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Quick Tip
Choose metric (kg and cm) or imperial (lb and inches).
About This Tool
Why use Advanced BMI?
Body mass index is weight in kilograms divided by height in metres squared. This calculator returns your BMI, the World Health Organization category it falls into, your BMI Prime and the weight range that would put you between 18.5 and 24.9.
BMI Prime is your BMI divided by 25, so 1.0 is the top of the healthy range: 0.92 means you are 8% below it, 1.15 means 15% above. BMI is a screening figure, not a diagnosis. It uses only height and weight, so it cannot tell muscle from fat — athletes often read as overweight, and it can understate body fat in older adults who have lost muscle.
Key Benefits
WHO categories, not invented bands
The cut-offs are the standard World Health Organization classifications used by clinicians worldwide.
BMI Prime for context
Your BMI as a ratio to the upper healthy limit, which makes it easy to see how far from the range you are.
Healthy weight range in your units
The 18.5–24.9 band converted into an actual weight range for your height.
How to use Advanced BMI
- 1
Choose metric (kg and cm) or imperial (lb and inches).
- 2
Enter your weight and height, plus age and sex for the supporting ranges.
- 3
Read your BMI and the WHO category: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30 and above obese.
- 4
Use the healthy weight range as a target band rather than a single number.
Best use cases
Check where your weight sits against the standard health categories.
Set a realistic target weight range rather than a single number.
Track progress across months alongside other measurements.
Convert a BMI mentioned by a doctor or an insurer into a weight you recognise.
Advanced BMI FAQs
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². For 70 kg at 1.75 m: 70 ÷ 3.0625 = 22.9. In imperial units it is weight (lb) ÷ height (in)² × 703.
What are the BMI categories?
Below 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25 to 29.9 is overweight and 30 or above is obese. Some health bodies apply lower thresholds for people of South Asian descent.
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so a muscular person can have a BMI in the overweight range with low body fat. Body fat percentage or waist measurement is a better guide in that case.
What is BMI Prime?
Your BMI divided by 25, the upper limit of the healthy range. A BMI Prime of 1.2 means your BMI is 20% above that limit.
Related Health Tools
More free health tools that work well alongside advanced bmi.