BMI calculator
Work out your body mass index from your height and weight, in metric or US units, and see where it falls on the adult scale.
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- Runs in your browser
- No uploads
Your BMI
Enter your height and weight to see your BMI.
- Runs on your deviceEvery tool works directly in your browser. No files are uploaded.
- Your privacy mattersYour files never leave your device, so there's nothing for us to store.
- No limitsUse any tool as much as you need. No daily caps, no waiting.
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How to use the BMI calculator
- Choose your units. Metric uses centimetres and kilograms; US uses feet, inches and pounds. Values carry over if you switch.
- Enter your height and weight. Your BMI, its category and the healthy weight range for your height appear as you type.
- Read it as a rough guide. The scale shows where the number sits between the category boundaries. It's an estimate for adults, not a diagnosis.
BMI formula and categories
BMI = weight (kg) ÷ height (m)². In US units it's 703 × weight (lb) ÷ height (in)². The calculator converts pounds and inches exactly (1 lb = 0.45359237 kg, 1 in = 2.54 cm), which gives the same answer to one decimal place.
| BMI | WHO adult category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 to 34.9 | Obesity class I |
| 35 to 39.9 | Obesity class II |
| 40 and over | Obesity class III |
Examples
Metric. 175 cm and 70 kg: 1.75² = 3.0625, and 70 ÷ 3.0625 = 22.86, shown as 22.9, a healthy weight. The healthy range at that height is 18.5 × 3.0625 = 56.7 kg up to 24.9 × 3.0625 = 76.3 kg.
US units. 5 ft 9 in is 69 inches. At 160 lb: 703 × 160 ÷ (69 × 69) = 112,480 ÷ 4,761 = 23.6.
What BMI doesn't tell you
BMI is a quick screening number that works across large groups of people. For one person it misses a lot: muscle versus fat, where fat is stored, age, sex and ethnicity. Waist measurement, blood pressure and blood tests say more about health risk than BMI alone.
This calculator is for adults aged 20 and over. It doesn't apply to children and teens, during pregnancy, or to very muscular people in the same way. It gives an estimate, not medical advice; talk to a doctor or nurse about your weight and health.
Frequently asked questions
How is BMI calculated?
Divide your weight in kilograms by your height in metres squared. At 70 kg and 1.75 m: 1.75 × 1.75 = 3.0625, and 70 ÷ 3.0625 = 22.9. In pounds and inches, multiply by 703: 703 × 160 lb ÷ (69 in × 69 in) = 23.6.
What is a healthy BMI?
For adults, the WHO calls 18.5 to 24.9 a healthy (normal) weight. Under 18.5 is underweight, 25 to 29.9 is overweight, and 30 or more is obesity, split into class I (30 to 34.9), class II (35 to 39.9) and class III (40 and over).
Can I use this BMI calculator for children or teens?
Not for the categories. Under 20, BMI is compared with growth charts for the same age and sex and given as a percentile. The adult cut-offs on this page don't apply, so use a child and teen BMI calculator or ask a doctor.
Why can BMI be misleading?
BMI uses only height and weight, so it can't tell muscle from fat or show where fat is carried. Muscular athletes can score as overweight, older adults who have lost muscle can score as healthy, and it doesn't apply during pregnancy. Some health bodies also suggest lower cut-offs for people of South Asian, Chinese and other Asian backgrounds.
Is my BMI rounded?
Yes, to one decimal place, and the category is taken from the rounded number you see. A BMI of 24.96 shows as 25.0 and is listed as overweight.