BMI & Body Fat Calculator
Calculate your Body Mass Index and body fat percentage free online
This page carries two health measures side by side. The BMI calculator works out your Body Mass Index from your height and weight in either metric or imperial units, and the body-fat estimate below it uses the US Navy tape-measure method. Both are quick screening tools rather than diagnoses, so treat the figures as a starting point for a conversation with a professional, not the last word.
Enter Your Measurements
Your BMI
<18.5Normal
18.5–24.9Overweight
25–29.9Obese
30+
BMI is a screening tool, not a diagnostic measure. Consult a healthcare professional for personalised advice.
🧮 How this is calculated ▼
BMI (Body Mass Index) divides your weight by the square of your height:
BMI = weight (kg) ÷ height (m)² · imperial: 703 × lbs ÷ in²
The WHO / NHS categories are: under 18.5 underweight · 18.5–24.9 healthy · 25–29.9 overweight · 30+ obese.
BMI is a quick population-level screening tool — it doesn't distinguish muscle from fat or account for build, so very muscular people can read as "overweight". Treat it as a rough guide, not a diagnosis.
❓ Frequently Asked Questions
What is BMI and how is it calculated? ▼
Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in metres (BMI = kg/m²). In imperial units, the formula is (weight in lbs ÷ height in inches²) × 703. It gives a single number used to broadly classify weight status.
What is a healthy BMI range? ▼
The World Health Organisation (WHO) defines a healthy BMI as 18.5 to 24.9. Below 18.5 is considered underweight, 25–29.9 is overweight, and 30 or above is classified as obese. These thresholds may differ slightly for certain ethnic populations.
Is BMI accurate for everyone? ▼
BMI is a useful population-level screening tool but has limitations for individuals. It doesn't distinguish between muscle and fat — a very muscular athlete may have a "high" BMI despite low body fat. It's also less reliable for children, the elderly, and pregnant women.
What is the BMI formula? ▼
Metric: BMI = weight (kg) ÷ height (m)². Imperial: BMI = (weight (lbs) ÷ height (inches)²) × 703. For example, a person who is 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75²) = 70 ÷ 3.0625 = 22.9.
What should I do if my BMI is outside the healthy range? ▼
BMI is a screening indicator only, not a medical diagnosis. If your BMI falls outside 18.5–24.9, speak to your GP or a healthcare professional who can assess your overall health using additional measurements like waist circumference, blood pressure, and blood tests.
🏃 Body Fat Calculator
U.S. Navy Method — uses body measurements to estimate body fat percentage
🎯 Ideal Weight Calculator
Your ideal body weight range based on height, using established medical formulas
🔧 More Tools
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