BMI Calculator
Enter your height and weight to get your body mass index (BMI), your weight category and the healthy weight range for your height. Works in kg/cm and lb/ft.
Enter your height and weight, then press Calculate BMI.
By Shah Rukh, software developer · Last updated:
What is BMI?
Body mass index (BMI) is a number that compares your weight with your height. It was devised in the 1830s by the Belgian mathematician Adolphe Quetelet and is now used worldwide by doctors, the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) as a quick way to screen adults for underweight, overweight and obesity.
BMI does not measure body fat directly. It is a simple estimate that works well across large groups of people, and it is a useful starting point for a conversation with a doctor about your weight.
BMI chart for adults
These are the WHO categories used by this calculator for adults aged 20 and over, for both men and women.
| BMI | Weight category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40.0 and above | Obesity class III (severe obesity) |
How to calculate BMI (formula)
You can calculate BMI by hand with one of these formulas:
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Worked example (metric)
Someone who is 175 cm tall and weighs 70 kg: 1.75 × 1.75 = 3.0625, and 70 ÷ 3.0625 = 22.9. That is in the healthy weight range.
Worked example (imperial)
Someone who is 5 ft 5 in (65 inches) and weighs 190 lb: 65 × 65 = 4,225, then 703 × 190 ÷ 4,225 = 31.6. That falls in obesity class I.
Healthy weight for your height
The calculator also turns the healthy BMI range (18.5 to 24.9) back into kilograms or pounds for your height. For example, at 170 cm the healthy weight range is about 53.5 kg to 72.0 kg; at 5 ft 10 in it is roughly 129 lb to 174 lb. If your weight is outside the range, the result tells you approximately how far away you are.
Limitations of BMI
- Muscle vs fat: BMI cannot tell them apart, so muscular people may be labelled overweight.
- Fat distribution: fat around the waist carries more health risk than fat elsewhere. Waist circumference or waist-to-height ratio adds useful information.
- Ethnicity: people of South Asian, Chinese and other Asian backgrounds often face higher risk of type 2 diabetes at lower BMIs, so lower cut-offs (23 and 27.5) are sometimes used.
- Age and pregnancy: adult categories do not apply to children, teens or pregnant women. Older adults may be healthier with a slightly higher BMI.
This BMI calculator is for general information and is not medical advice. Talk to a doctor or registered dietitian before making big changes to your diet or exercise routine.
BMI for children and teens
For ages 2 to 19, the same formula is used, but the number is then compared with other children of the same age and sex on a growth chart. The result is a percentile: below the 5th percentile is underweight, 5th to below the 85th is healthy, 85th to below the 95th is overweight, and the 95th percentile or above is obesity. If you enter an age under 20, the calculator reminds you of this.
Frequently asked questions
What is a healthy BMI?
For adults, a BMI from 18.5 to 24.9 is considered a healthy weight by the World Health Organization. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or more is obesity.
Is BMI different for men and women?
No. Adults use the same formula and the same categories regardless of sex. Women naturally carry more body fat than men at the same BMI, which is one reason BMI is only a screening tool.
Does age change my BMI result?
For adults 20 and older, the categories are the same at every age. For children and teens aged 2 to 19, BMI has to be compared with growth charts for age and sex, and the result is given as a percentile.
Why is my BMI high when I am muscular?
BMI only uses height and weight, so it cannot tell muscle from fat. Athletes and people who lift weights can have a high BMI and still have low body fat.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. For example, 160 lb at 5 ft 8 in (68 in): 160 × 703 ÷ 4,624 = 24.3.
Are BMI cut-offs different for Asian people?
Research shows that many people of Asian descent face higher health risks at lower BMIs. Some health bodies therefore use 23 as the start of increased risk and 27.5 as high risk for Asian populations.