Body mass index with category and healthy weight range.
Your body mass index takes seconds to find with this BMI calculator, using your height and weight in US units (feet, inches and pounds) or metric (centimetres and kilograms). Along with your BMI, it shows your weight category, the healthy weight range for your height, your BMI Prime, and how much weight would bring you into the healthy range. A gauge and a BMI chart show where you sit at a glance. It is designed for adults aged 20 and over.
How to Use the BMI Calculator
- Choose US or metric units with the toggle.
- Enter your height and weight.
- Read your BMI and its category, then look at the healthy weight range for your height and the table below the gauge.
The BMI Formula
- Metric: BMI = weight (kg) ÷ height (m)²
- US units: BMI = 703 × weight (lb) ÷ height (in)²
BMI Prime is your BMI divided by 25, the upper limit of the healthy range. A BMI Prime below 1.0 means you are under that limit.
BMI Categories for Adults
The calculator uses the World Health Organization’s classification for adults:
| BMI | 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 |
BMI Examples
US units. Someone 5 ft 9 in (69 inches) tall who weighs 160 lb: BMI = 703 × 160 ÷ 69² = 112,480 ÷ 4,761 = 23.6, in the healthy range. At this height, the healthy range is about 125 to 169 lb.
Metric. Someone 175 cm tall who weighs 70 kg: BMI = 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9. The healthy range at 175 cm is about 56.7 to 76.3 kg, and the BMI Prime is 0.91.
What BMI Does Not Tell You
BMI is a quick screening number, not a diagnosis. It uses only height and weight, so it has known limits:
- It does not separate muscle from fat. Athletes and very muscular people can have a high BMI with little body fat.
- It does not show where fat is stored. Fat around the waist carries more health risk than fat elsewhere. Waist measurement adds useful information.
- It can read differently with age. Older adults tend to lose muscle, so the same BMI can mean more body fat.
- Ethnicity matters. Some groups, including many people of South Asian, Chinese and other Asian backgrounds, face higher health risks at lower BMIs. Some health bodies use lower cut-offs for these groups.
A doctor will look at BMI together with other measures, such as waist size, blood pressure and blood tests.
BMI for Children and Teens
For people aged 2 to 19, BMI is compared with growth charts for the child’s age and sex, and reported as a percentile. The adult categories above do not apply, so this calculator should not be used for children. Ask a pediatrician or use a dedicated child BMI percentile tool.
Beyond BMI
- For a target weight based on several formulas, use the ideal weight calculator.
- To estimate how much of your weight is fat, use the body fat calculator.
- To see how many calories you need to maintain or change your weight, use the calorie calculator.
BMI Questions
What is a healthy BMI?
For most adults, a BMI from 18.5 to 24.9 is considered healthy under the WHO classification.
Is BMI accurate?
BMI is a reasonable guide for most adults at a population level, but it can misclassify individuals, especially very muscular people and older adults. Use it as a starting point, not a final answer.
Is BMI different for men and women?
The formula and the adult categories are the same for men and women. Women usually carry more body fat than men at the same BMI.
How much weight should I lose to reach a healthy BMI?
If your BMI is 25 or more, the calculator shows how much weight would bring you to a BMI of 24.9. Talk to your doctor before starting a weight loss plan.
How we checked this page: the categories match the WHO adult classification, the examples were worked by hand, and the healthy weight ranges were confirmed in the calculator.
Sources: World Health Organization, “A healthy lifestyle – WHO recommendations” (BMI classification for adults); Centers for Disease Control and Prevention, “About Adult BMI” and “About Child and Teen BMI”.
This calculator is for general information only and is not medical advice. Speak to a doctor or another qualified health professional about your weight and health.