BMI calculator
Health & fitnessWhat is your body mass index (BMI)?
Your BMI and its WHO adult category, the normal-weight range for your height, and what BMI cannot tell you.
Height and weight
What you enter stays on your device while you use this tool. Opening a shared link sends the settings in its address to HowToolbox to prepare the page.
For your height
- A BMI of 18.5–24.9 corresponds to about 125 lb to 169 lb.
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Adult BMI categories
For adults aged 18 and over. Your category is marked.
| Category | BMI (kg/m²) |
|---|---|
| Underweight | below 18.5 |
| Normal weight | 18.5–24.9 |
| Overweight | 25.0–29.9 |
| Obesity class I | 30.0–34.9 |
| Obesity class II | 35.0–39.9 |
| Obesity class III | 40.0 or more |
What BMI cannot tell you
- These categories are for adults. Children and teenagers are assessed with BMI-for-age, which compares them with others of the same age and sex.
- BMI does not separate muscle from fat or show where fat sits. Muscular people can score high, and it is not meant for use in pregnancy.
- The same BMI can carry different health risks for different people. For some ethnic backgrounds, risks start at a lower BMI.
- BMI is a quick screening number, not a diagnosis. A health professional looks at the whole picture.
Your BMI and its WHO adult category, the normal-weight range for your height, and what BMI cannot tell you.
How to use
- Choose centimetres and kilograms, or feet, inches and pounds.
- Enter your height and weight.
- Read your BMI, its adult category and the weight range that matches a BMI of 18.5–24.9 for your height.
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How it works
Body mass index compares weight with height. It is a quick way to screen groups of adults for weight that may affect health, and the same cut-offs are used around the world, so results can be compared.
BMI = weight in kilograms ÷ (height in metres)². For example, 70 kg at 1.75 m gives 70 ÷ 1.75² = 22.9. The WHO adult categories are: under 18.5 underweight, 18.5–24.9 normal weight, 25.0 and over overweight, 30.0 and over obesity; obesity is often split into class I (30.0–34.9), class II (35.0–39.9) and class III (40.0 and over). Sources: WHO and Statistics Canada.
BMI is only a starting point. It cannot tell muscle from fat, it says nothing about where fat sits, and the risk at a given BMI differs between people and ethnic backgrounds. For children and teenagers, WHO uses BMI-for-age reference charts instead of these adult cut-offs.
Worked example
What is the BMI at 81 kg and 1.8 m?
- Square the height: 1.8 × 1.8 = 3.24.
BMI = 81 ÷ 3.24 = 25.0.
Frequently asked questions
Can I use this for my child?
No. Children's BMI changes as they grow, so it is compared with others of the same age and sex using BMI-for-age charts. Ask your child's health nurse or doctor.
I'm muscular and my BMI says overweight. Is it wrong?
It may be. Muscle weighs more than fat for its size, so athletes often have a high BMI without extra fat. A waist measurement or a health check gives a fuller picture.
Why is my result rounded to one decimal?
The category limits are given to one decimal, so the result is shown and classified the same way: a BMI of 24.96 shows as 25.0 and counts as overweight.
Is BMI calculated differently for women and men?
No. The formula and the adult categories are the same for both. At the same BMI, women usually have more body fat than men, so a waist measurement adds useful context.
What is a healthy weight for my height?
Multiply your height in metres, squared, by 18.5 and by 24.9: at 1.70 m that is about 53.5 to 72 kg. The calculator shows this normal-weight range for your height.
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