BMI Calculator
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BMI basics
What Is BMI?
BMI, or Body Mass Index, is a quick screening measure that compares body weight with height. It can help place an adult into a standard weight category, but it does not tell the full story about health.
BMI categories
Adult BMI Categories
These are the standard adult BMI categories used by the calculator for people age 20 and older.
| Category | BMI Range | Health Risk |
|---|---|---|
| Underweight | Below 18.5 | Increased risk of nutrient deficiency |
| Healthy weight | 18.5 – 24.9 | Lowest baseline risk |
| Overweight | 25.0 – 29.9 | Mildly elevated risk |
| Obese (Class I) | 30.0 – 34.9 | Moderate risk |
| Obese (Class II) | 35.0 – 39.9 | High risk |
| Obese (Class III) | 40.0+ | Very high risk |
Getting started
How to Use This BMI Calculator
Use the calculator for a quick adult BMI estimate, then read the category and explanation as screening context.
- 1
Enter your height
You can use feet/inches or centimeters.
- 2
Enter your weight
You can use pounds or kilograms.
- 3
Calculate BMI
Click Calculate BMI to generate your BMI number and category.
- 4
Review the result
Check your BMI number, weight category, BMI Prime, and healthy weight range.
- 5
Use the explanation carefully
Read the result as a general screening guide, not as a medical diagnosis.
The math
BMI Formula
The calculator supports both metric and US customary units. Both formulas return BMI in kg/m².
Metric units formula
Used with kilograms and meters or centimeters.
US customary units formula
Used with pounds and inches.
Example
BMI Calculation Example
This example shows how the BMI formula works before you enter your own values.
| Step | Value |
|---|---|
| Example input | 70 kg at 1.75 m |
| Formula | BMI = 70 / 1.75² |
| Result | BMI = 22.9, which falls in the healthy weight range for most adults. |
Youth growth assessment
BMI for Children and Teenagers
For children and teenagers, BMI is interpreted differently from adults. Children and teens are usually assessed using age-and-sex percentiles, not only the adult BMI category table.
Growth rates differ between genders and at different ages, which is why a growth chart standard from bodies like the WHO or CDC is used to track growth curve percentiles.
Use cases
When to Use This BMI Calculator
BMI is useful because it is quick, low-cost, and simple. It works best as a first screening step, not as the final answer about health.
- Check weight category
- Instantly check if your body mass falls within standard health classifications.
- Track weight changes
- Monitor weight variations over long-term fitness or wellness regimes.
- Estimate height balance
- Find out if your body weight is high, low, or proportionate for your specific height.
- Standard comparison
- Compare your metric/US indexes with standard adult BMI categories globally.
- Initiate fitness plan
- Formulate baseline references before starting diet plans or physical exercise schemes.
- Signal checkups
- Identify whether you may need to schedule a comprehensive physical checkup with a GP.
Clinical limits
Accuracy and Limitations of BMI
BMI is helpful, but it does not directly measure body fat or show how much of your weight comes from muscle, bone, water, or fat.
- BMI may be less accurate for
- Athletes or bodybuilders, pregnant individuals, older adults, children and teenagers, people with low or high muscle mass, and diverse ethnicities.
- Pair BMI with other tools
- Waist circumference, waist-to-height ratio, blood pressure levels, cholesterol profile, blood sugar levels, and diet quality can give better context.
- Use clinical context
- BMI alone does not diagnose health. Healthcare providers usually consider medical history, physical examination, and lab findings too.
Target range
Healthy Weight Range from BMI
For adults, the healthy BMI range is generally 18.5 to less than 25. You can estimate a healthy weight range for your height using standard multipliers.
Healthy BMI weight range
Use 18.5 for the lower estimate and 24.9 for the upper estimate.
| Metric | Value |
|---|---|
| Example height | 1.75 m |
| Minimum healthy weight | 18.5 × 1.75² = 56.7 kg |
| Maximum healthy weight | 24.9 × 1.75² = 76.3 kg |
| Estimated healthy range | About 56.7 kg to 76.3 kg |
Health context
Health Risks to Keep in Mind
BMI categories are screening categories. If your result is outside the healthy range, use it as a prompt to review broader health signals with a qualified professional.
- Risks: Overweight & Obesity
- Being overweight increases the risk of serious diseases and health conditions, including high blood pressure, high LDL and low HDL cholesterol, Type II Diabetes, coronary heart disease and stroke, sleep apnea and breathing issues, osteoarthritis, clinical depression, anxiety, and low quality of life.
- Risks: Underweight
- Being underweight can involve malnutrition, vitamin deficiencies and anemia, osteoporosis, decreased immune functions, growth and developmental delays in children/teens, reproductive issues, postoperative surgery complication risks, and elevated risk of mortality compared to healthy BMIs.
Next checks
Use BMI with Other Calculators
For a more complete picture, pair your BMI with body composition, calorie, and macro estimates.
Try the Body Fat Calculator, Calorie Calculator, and Macro Calculator to plan a balanced approach.
Frequently Asked Questions
The World Health Organization classifies a BMI between 18.5 and 24.9 as a healthy weight range for most adults. Below 18.5 is considered underweight, 25.0–29.9 is overweight, and 30.0 or higher is obese. These ranges are general guidelines and do not replace medical advice.
BMI does not distinguish between fat and muscle. Athletes and people with high muscle mass often have a BMI in the overweight range despite having low body fat. For these individuals, body fat percentage, waist-to-hip ratio, or DEXA scans give a more accurate picture of health than BMI alone.
BMI = weight (kg) ÷ height (m)². In imperial units, BMI = (weight in lbs × 703) ÷ height (in)². Our calculator does this for you automatically using either US or metric units.
The BMI formula is identical for adult men and women. However, women typically carry a slightly higher percentage of body fat at the same BMI, so context matters. Children and teens use age- and sex-specific BMI percentile charts instead.
A BMI of 30.0 or higher is classified as obese. Class I obesity is 30.0–34.9, Class II is 35.0–39.9, and Class III (severe obesity) is 40.0 and above. Higher BMI ranges are associated with greater risk of diabetes, heart disease, and other conditions.
BMI is a useful screening tool but a poor goal in isolation. Pair it with body fat percentage, waist circumference, strength benchmarks, and how you feel. Use our Body Fat Calculator and Ideal Weight Calculator for a fuller picture.
Children and teens grow at different rates, so absolute BMI values are not meaningful. Pediatricians use BMI-for-age percentile charts that compare a child's BMI against peers of the same age and sex.
Medical note
BMI Calculator Disclaimer
This BMI calculator is designed for general educational use. It is based on standard BMI formulas and adult BMI category guidance from trusted health sources such as CDC, NHS, Mayo Clinic, and Cleveland Clinic.
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