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BMI Calculator
Use this free BMI calculator to find your Body Mass Index, see which weight category you fall into, and learn what a healthy weight range looks like for your height. Works in metric and US units, and updates instantly.
BMI Calculator
Your Result
BMI is a screening tool, not a diagnosis. Results are estimates for adults aged 20 and over.
What Is BMI (Body Mass Index)?
Body Mass Index (BMI) is a number calculated from your height and weight. It is widely used as a quick, low-cost way to screen whether a person is underweight, at a healthy weight, overweight, or obese for their height. The result is measured in kilograms per square metre (kg/m²).
The idea goes back to the Belgian mathematician Adolphe Quetelet in the 1800s, which is why it was once called the Quetelet index. The term “Body Mass Index” was popularised in 1972 by the physiologist Ancel Keys. Today the World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) both use BMI as a screening tool.
BMI is useful because it needs only two measurements, but it is an indicator, not a diagnosis. It does not measure body fat directly, so it should be read together with other health information.
How to Use This BMI Calculator
- Choose Metric (centimetres and kilograms) or US (feet, inches and pounds).
- Enter your age if you like. The age field matters mainly for teens, because adult categories do not apply under 20.
- Enter your height and weight. The result updates as you type, or you can press Calculate BMI.
- Read your BMI, your category, your healthy weight range, your BMI Prime and your Ponderal Index. The tool also shows how much weight sits between you and the healthy range.
Everything runs in your browser. Your numbers are never sent to a server or stored.
BMI Table for Adults
This is the WHO classification of adult weight status. It applies to men and women aged 20 and over.
| Classification | BMI range (kg/m²) |
|---|---|
| Severe thinness | Below 16 |
| Moderate thinness | 16 – 16.9 |
| Mild thinness | 17 – 18.4 |
| Normal weight | 18.5 – 24.9 |
| Overweight (pre-obese) | 25 – 29.9 |
| Obese class I | 30 – 34.9 |
| Obese class II | 35 – 39.9 |
| Obese class III | 40 and above |
Note for Asian populations: the WHO has observed that health risks can rise at lower BMI values in many Asian groups and suggests public health action points at 23 and 27.5. Some countries use their own cut-offs, so ask a local healthcare professional which applies to you.
BMI for Children and Teens (Ages 2 to 19)
Children and teens are still growing, and body fat changes with age and differs between boys and girls. For this reason the CDC does not use the adult cut-offs. Instead, a child’s BMI is compared with other children of the same age and sex and expressed as a percentile.
| Category | Percentile range |
|---|---|
| Underweight | Below the 5th percentile |
| Healthy weight | 5th to less than the 85th percentile |
| Overweight | 85th to less than the 95th percentile |
| Obesity | 95th percentile or above |
This calculator will still show a BMI number if you enter an age between 2 and 19, but it will remind you that the percentile on a CDC growth chart is what counts. A paediatrician can plot this for you. You can also read more on the CDC BMI page.
Healthy Weight Range by Height
The table below shows the weight range that corresponds to a BMI of 18.5 to 24.9 for common adult heights.
| Height | Height (cm) | Healthy weight (lb) | Healthy weight (kg) |
|---|---|---|---|
| 4' 10" | 147 cm | 89 – 119 lb | 40.2 – 54.0 kg |
| 4' 11" | 150 cm | 92 – 123 lb | 41.5 – 55.9 kg |
| 5' 0" | 152 cm | 95 – 127 lb | 43.0 – 57.8 kg |
| 5' 1" | 155 cm | 98 – 132 lb | 44.4 – 59.8 kg |
| 5' 2" | 157 cm | 101 – 136 lb | 45.9 – 61.8 kg |
| 5' 3" | 160 cm | 104 – 141 lb | 47.4 – 63.8 kg |
| 5' 4" | 163 cm | 108 – 145 lb | 48.9 – 65.8 kg |
| 5' 5" | 165 cm | 111 – 150 lb | 50.4 – 67.9 kg |
| 5' 6" | 168 cm | 115 – 154 lb | 52.0 – 70.0 kg |
| 5' 7" | 170 cm | 118 – 159 lb | 53.6 – 72.1 kg |
| 5' 8" | 173 cm | 122 – 164 lb | 55.2 – 74.3 kg |
| 5' 9" | 175 cm | 125 – 169 lb | 56.8 – 76.5 kg |
| 5' 10" | 178 cm | 129 – 174 lb | 58.5 – 78.7 kg |
| 5' 11" | 180 cm | 133 – 179 lb | 60.2 – 81.0 kg |
| 6' 0" | 183 cm | 136 – 184 lb | 61.9 – 83.3 kg |
| 6' 1" | 185 cm | 140 – 189 lb | 63.6 – 85.6 kg |
| 6' 2" | 188 cm | 144 – 194 lb | 65.4 – 88.0 kg |
| 6' 3" | 190 cm | 148 – 199 lb | 67.1 – 90.4 kg |
| 6' 4" | 193 cm | 152 – 205 lb | 68.9 – 92.8 kg |
BMI Formula
BMI is weight divided by height squared. The formula depends on the units you use. The examples below use a person who is 5 feet 10 inches (70 inches, or 1.778 m) tall and weighs 160 pounds (72.57 kg).
Metric (SI) formula
US customary formula
Both give the same answer. The number 703 is the conversion factor between pounds per square inch and kilograms per square metre.
BMI Prime
BMI Prime is the ratio of your BMI to the upper limit of the normal range, which is 25. It is a unitless number that shows at a glance how far you are above or below that limit.
| Classification | BMI | BMI Prime |
|---|---|---|
| Severe thinness | Below 16 | Below 0.64 |
| Moderate thinness | 16 – 17 | 0.64 – 0.68 |
| Mild thinness | 17 – 18.5 | 0.68 – 0.74 |
| Normal | 18.5 – 25 | 0.74 – 1.0 |
| Overweight | 25 – 30 | 1.0 – 1.2 |
| Obese class I | 30 – 35 | 1.2 – 1.4 |
| Obese class II | 35 – 40 | 1.4 – 1.6 |
| Obese class III | Above 40 | Above 1.6 |
Because it is a ratio, BMI Prime makes it easy to compare groups that use different upper limits, for example populations where the cut-off is 23 instead of 25.
Ponderal Index
The Ponderal Index (PI) is a close relative of BMI. The only difference is that height is cubed instead of squared. Because a person’s volume grows roughly with the cube of their height, the PI is considered more reliable than BMI for people who are very tall or very short.
Like BMI, the Ponderal Index is a population-level screening measure and does not separate muscle from fat.
Health Risks Associated With Being Overweight
According to the CDC, a higher BMI is linked with an increased risk of several conditions, including:
- High blood pressure
- Higher LDL (“bad”) cholesterol, lower HDL (“good”) cholesterol and high triglycerides
- Type 2 diabetes
- Coronary heart disease and stroke
- Gallbladder disease
- Osteoarthritis
- Sleep apnea and breathing problems
- Some cancers, including endometrial, breast, colon, kidney, gallbladder and liver cancer
- Lower quality of life, and mental health conditions such as depression and anxiety
- Body pain and difficulty with some physical activities
These are associations at the population level. Many people with a higher BMI are healthy, and many with a normal BMI are not. Your own risk depends on the full picture.
Health Risks Associated With Being Underweight
Being underweight also carries risks:
- Malnutrition, vitamin deficiencies and anaemia
- Osteoporosis and a higher risk of broken bones
- A weaker immune system
- Growth and development problems in children and teens
- Hormonal changes that can disrupt periods, and a higher chance of complications in pregnancy
- More risk of complications after surgery
Being underweight can sometimes signal an underlying condition, such as a digestive disorder, thyroid problem or an eating disorder. If you are underweight and do not know why, speak to a doctor.
Limitations of BMI
BMI is a simple estimate and cannot capture everything about your health.
- It does not separate muscle from fat. Athletes and people with a lot of muscle can be classed as overweight while having a low body fat percentage.
- It ignores where fat is stored. Fat around the waist carries more health risk than fat on the hips and thighs, which BMI cannot show. Waist circumference gives extra information.
- Age and sex matter. Older adults tend to carry more body fat than younger adults at the same BMI, and women tend to carry more than men.
- Ethnicity matters. Body composition and risk differ between groups, which is why some countries use different cut-offs.
- It is not designed for pregnancy or for children without age-based percentiles.
Even with these limits, BMI is a reasonable indicator of excess weight for most of the population, and it works best alongside other measures.
What to Do With Your BMI Result
If your BMI is in the healthy range, keep up regular physical activity, balanced eating and enough sleep. If it is above or below the healthy range, treat it as a prompt for a conversation with a doctor or dietitian, not as a verdict. They may suggest further checks such as waist measurement, blood pressure, blood sugar and cholesterol.
To plan next steps, try our BMR Calculator to estimate how many calories your body uses at rest, and our Calorie Calculator to estimate daily needs.
Medical disclaimer: this calculator is for general information only and is not medical advice, diagnosis or treatment. Always speak to a qualified healthcare professional about your health. Sources: World Health Organization and US Centers for Disease Control and Prevention.
Frequently Asked Questions
What is a good BMI?
For most adults, a BMI between 18.5 and 24.9 is classed as a healthy or normal weight by the World Health Organization. A BMI below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese.
How do I calculate my BMI?
Divide your weight in kilograms by your height in metres squared. In US units, multiply your weight in pounds by 703 and divide by your height in inches squared. Our calculator does this for you instantly in either unit system.
Is BMI the same for men and women?
The adult BMI formula and the WHO categories are the same for men and women. However, women tend to carry more body fat than men at the same BMI, so BMI should be read alongside other measurements.
Is BMI accurate for athletes and muscular people?
Not always. BMI measures weight relative to height and cannot tell muscle from fat. Athletes and very muscular people can have a high BMI without excess body fat.
What is a healthy BMI for children and teens?
For ages 2 to 19, BMI is interpreted as a percentile for age and sex using CDC growth charts. A healthy weight is the 5th percentile up to below the 85th percentile. The adult cut-offs do not apply.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the normal range. A value below 0.74 is underweight, 0.74 to 1 is normal, and above 1 is overweight.
What is the Ponderal Index?
The Ponderal Index divides weight in kilograms by height in metres cubed. It is similar to BMI but is considered more reliable for very tall or very short people.
Does BMI work for older adults?
BMI can be used, but older adults tend to carry more body fat and less muscle than younger adults at the same BMI. A doctor can help interpret the number for your age and health.
Do the BMI cut-offs differ for Asian populations?
Yes. The WHO notes that Asian populations can face higher health risks at lower BMI values, and suggests public health action points of 23 and 27.5. Many Asian countries use their own cut-offs.
Can BMI diagnose a health condition?
No. BMI is a screening tool, not a diagnosis. A healthcare professional will also look at waist size, blood pressure, blood tests, family history and lifestyle.