BMI Calculator
Calculate Body Mass Index with metric and imperial units and health category.
About the BMI Calculator
Calculate your Body Mass Index (BMI) in seconds using metric (cm and kg) or imperial (inches and pounds). Enter your height and weight and the calculator shows your BMI, your WHO weight category and the healthy weight range for your height — updating instantly as you type.
BMI is a quick screening measure used by doctors and health organisations worldwide. It isn’t a diagnosis, but it’s a useful starting point for understanding whether your weight is in a healthy range.
How to use the BMI Calculator
- 1Choose Metric (cm/kg) or Imperial (in/lb).
- 2Enter your height and weight.
- 3Read your BMI, category and healthy weight range instantly.
- 4Change the values to see how a different weight would affect your BMI.
How do we calculate BMI?
BMI compares your weight with the square of your height. The metric formula is BMI = weight (kg) ÷ height (m)². The imperial formula is BMI = 703 × weight (lb) ÷ height (in)². Two worked examples:
- Metric: 70 kg and 170 cm → 70 ÷ (1.70 × 1.70) = 24.2
- Imperial: 154 lb and 67 in (5′7″) → 703 × 154 ÷ (67 × 67) = 24.1
BMI categories for adults
The World Health Organization uses these ranges for adults aged 20 and over:
- Below 18.5 — Underweight
- 18.5 to 24.9 — Normal weight
- 25.0 to 29.9 — Overweight
- 30.0 and above — Obese
Limitations of BMI
BMI doesn’t distinguish muscle from fat, so athletes can appear “overweight”. It also ignores where fat is stored, and healthy ranges can vary with age, sex and ethnicity. Children and teens need age-specific BMI percentiles. Always speak to a healthcare professional about your personal health.
Guides & tutorials
How Many Calories Should I Eat a Day? BMR & TDEE Explained
Work out how many calories you need a day to maintain, lose or gain weight. BMR and TDEE explained simply, with the formula and a worked example.
How Do We Calculate BMI? Formula, Examples & Chart
How to calculate BMI in kg/m and lb/in, with step-by-step worked examples, the adult BMI chart, healthy weight ranges and the limits of BMI.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight range.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. Select Imperial above and the calculator does it for you.
Is BMI different for men and women?
The adult formula and categories are the same for men and women, although body-fat levels at a given BMI tend to differ.
Can I use this BMI calculator for children?
No. Children and teenagers should use BMI-for-age percentile charts, because healthy ranges change as they grow.
Is BMI Calculator free to use?
Yes — BMI Calculator is completely free with no signup, no limits and no hidden costs.
Is my data private and secure?
Everything runs entirely in your browser — your files and text never leave your device, ensuring complete privacy.
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