BMI Calculator (Metric and Imperial)
Body mass index (BMI) relates weight to height. Use the metric form (kilograms and centimeters) or the imperial form (pounds, feet and inches). The categories apply to adults aged 20 and over.
Metric
- Your BMI
- 22.9
- Category
- Healthy weight
- Healthy weight for your height
- 56.7 – 76.3 kg
Imperial
- Your BMI
- 24.3
- Category
- Healthy weight
- Healthy weight for your height
- 122 – 164 lb
How it’s calculated
BMI is weight in kilograms divided by the square of height in meters:
BMI = weight (kg) ÷ height (m)²
In imperial units the same result is BMI = 703 × weight (lb) ÷ height (in)². This calculator converts pounds and inches to metric with the exact factors, which is equivalent.
Adult categories used by the World Health Organization: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, and 30 or more obesity.
Examples
Metric
A person who weighs 70 kg and is 175 cm (1.75 m) tall has a BMI of 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9, in the healthy weight range. For that height, 18.5 to 24.9 corresponds to about 56.7 to 76.3 kg.
Imperial
A person who weighs 160 lb and is 5 ft 8 in (68 in) tall has a BMI of 703 × 160 ÷ 68² ≈ 24.3, also in the healthy weight range.
Frequently asked questions
What is a healthy BMI?
For adults, the World Health Organization classifies a BMI from 18.5 to 24.9 as a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obesity.
Is BMI accurate for everyone?
BMI is a quick screening number, not a diagnosis. It does not tell muscle from fat, so very muscular people can score high. It also says nothing about where fat is stored, and some health bodies use lower cut-offs for people of Asian descent.
Can I use this for children or teens?
No. For people under 20, BMI is interpreted with age- and sex-specific growth charts (BMI-for-age percentiles), not the adult categories. Ask a pediatrician or use a child BMI chart.
Why does the imperial formula use 703?
One pound is 0.45359237 kg and one inch is 0.0254 m. Converting lb/in² to kg/m² multiplies by about 703.07, so 703 is the rounded conversion factor.
What should I do if my BMI is outside the healthy range?
Treat it as a prompt for a conversation, not a verdict. A doctor can look at waist size, blood pressure, blood tests and your history to judge whether your weight affects your health.
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Results are estimates for general information and are not financial, medical or legal advice.