BMI Calculator

What is BMI (Body Mass Index)?

Body Mass Index (BMI) is a simple ratio of your weight to your height. It is widely used as a quick screening tool to suggest whether an adult may be underweight, at a healthy weight, overweight, or living with obesity. This calculator applies the standard adult BMI formula and compares your result with commonly used categories from public health organizations such as the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC).

Although BMI does not measure body fat directly, it provides an accessible way to put your height and weight into context and start a conversation about health risks and goals with a qualified professional.

BMI formulas

The calculator accepts either metric or imperial units and converts them internally to use the standard formulas.

Metric BMI formula

When you enter weight in kilograms (kg) and height in meters (m), BMI is calculated as:

In plain language, your weight in kilograms is divided by your height in meters squared (height × height).

Imperial BMI formula

If you prefer pounds and inches, BMI is calculated as:

BMI = (weight in pounds ÷ (height in inches)²) × 703

The factor 703 simply converts the imperial units into the same scale used for metric BMI values.

BMI categories and comparison table

Your BMI value is compared with standard adult BMI ranges. The table below summarizes common cutoffs used for people aged 18 and older:

Different countries and guidelines sometimes use slightly different labels or cutoffs. This calculator uses widely referenced adult cutoffs for general information purposes.

How to use the BMI calculator

1. Enter your weight and choose kilograms (kg) or pounds (lb).
2. Enter your height and select centimeters (cm) or inches (in). If you know your height in feet and inches, convert to total inches before entering, or use centimeters.
3. Optional: add a target weight. The calculator can show what your BMI would be at a goal weight, which may help you visualize realistic changes.
4. Optional: enter age, gender, and activity level. These values are used to estimate your basal metabolic rate (BMR) and approximate daily calorie needs, not to compute BMI itself.
5. Select the button to calculate. The tool displays your BMI value, your category, and any additional estimates supported by the inputs you provided.

You can repeat the calculation as often as you like to explore how changes in weight affect BMI and category.

Worked example

Suppose an adult weighs 72 kg and is 1.75 m tall.

• Weight = 72 kg
• Height = 1.75 m

Using the metric formula:

BMI = 72 ÷ (1.75 × 1.75) = 72 ÷ 3.0625 ≈ 23.5

A BMI of about 23.5 falls in the 18.5–24.9 range, which is classified as a healthy weight for most adults. If this person entered a target weight of 80 kg at the same height, their target BMI would be:

BMI = 80 ÷ 3.0625 ≈ 26.1, which is in the overweight range. This comparison shows how even moderate weight changes can move someone between categories.

BMR and daily calorie needs

The additional fields for age, gender, and activity level allow the calculator to estimate how many calories your body may use each day.

• Basal Metabolic Rate (BMR) is an estimate of how many calories your body would use in 24 hours at complete rest, just to keep vital functions running (breathing, circulation, basic cell processes).
• Total Daily Energy Expenditure (TDEE) adjusts BMR for your typical activity level and provides an approximate number of calories you might burn in a usual day.

In general:

• Consuming roughly the same number of calories as your TDEE tends to maintain weight.
• Eating fewer calories than your TDEE over time may lead to weight loss.
• Eating more than your TDEE may lead to weight gain.

Safe and sustainable changes are typically modest (for example, a small daily deficit or surplus), and the right approach depends on your health history. Use these numbers as rough guides only, and discuss any significant weight-change plan with a healthcare professional or registered dietitian.

Interpreting your BMI result

Your BMI is only one piece of information about your health. Consider the following when interpreting your result:

• Underweight (< 18.5) – This may be associated with undernutrition, certain illnesses, or other health concerns. If you are underweight and did not intend to lose weight, speak with a health professional.
• Healthy weight (18.5–24.9) – For many adults, this range is associated with lower risk of heart disease, stroke, and type 2 diabetes, especially when combined with other healthy habits.
• Overweight (25.0–29.9) – Risk of weight-related conditions may be higher. Gradual changes to diet, movement, sleep, and stress can be helpful, alongside medical advice if you have other risk factors.
• Obesity (30.0 and above) – The likelihood of health complications usually increases as BMI rises. A personalized plan created with your doctor or a specialist can help you address risks safely.

Children and teenagers use age- and sex-specific BMI percentile charts, not the fixed adult cutoffs shown here. This calculator is not designed for users under 18.

Beyond BMI: other health indicators

BMI does not tell the whole story. Other measurements and tests can provide important additional context, including:

• Waist circumference and waist-to-height ratio – give clues about abdominal fat, which is closely linked with metabolic risk.
• Body fat percentage – estimates how much of your weight is fat versus lean mass.
• Blood pressure, blood sugar, and cholesterol – help assess cardiovascular and metabolic health.
• Fitness measures – such as strength, endurance, and flexibility.

When possible, review your BMI result together with these other indicators and your personal and family medical history.

Limitations, assumptions, and medical disclaimer

This BMI calculator has important limitations and is based on several assumptions:

• Designed for adults. The calculations and categories are intended for people aged 18 and older. They are not appropriate for infants, children, or teenagers.
• Does not distinguish muscle from fat. Athletic and very muscular people may have a high BMI even when their body fat is low. Older adults or people with low muscle mass may have a normal BMI but higher body fat.
• Does not account fully for ethnicity, sex, or body type. Health risks at a given BMI can differ between populations. Some groups may experience higher risk at lower BMI values.
• Pregnancy and certain medical conditions. BMI is not a good indicator during pregnancy or in some medical situations (for example, severe fluid retention).
• Standard adult cutoffs. The tool uses commonly referenced adult BMI thresholds. Different guidelines or clinical contexts may use slightly different ranges or terminology.

Medical disclaimer: This calculator provides educational information only and does not offer medical diagnosis, treatment, or individualized nutrition advice. Do not make major health decisions based solely on a BMI value or on any estimates from this tool. Always consult a qualified healthcare professional if you have concerns about your weight, eating patterns, exercise, or overall health.

If your BMI or symptoms worry you, or if you are planning significant weight loss or gain, discuss your situation with your doctor or another licensed clinician who can review your full medical history and run appropriate tests.

About this calculator

This tool uses the standard adult BMI formula and typical public health cutoffs similar to those published by organizations such as the WHO and CDC. BMR and daily energy estimates, when provided, are based on commonly used predictive equations and broad activity categories. All values are approximate and may differ from measurements obtained in a clinical setting.