BMI Calculator
Understanding adult BMI (Body Mass Index)
Body Mass Index (BMI) relates body weight to height squared and is used as a quick adult screening measure. This calculator uses your weight and height to estimate BMI and place it in commonly used adult ranges, such as underweight, normal weight, overweight, and obesity classes. BMI does not measure body fat directly and should be considered alongside other health information and professional guidance.
By putting height and weight on the same scale, an adult BMI estimate can offer a starting point for discussing health risks or goals with a qualified professional.
Adult BMI formulas in metric and imperial units
This BMI calculator accepts metric or imperial height and weight entries, then converts them to the standard BMI scale.
Metric BMI formula for kilograms and meters
When you enter weight in kilograms (kg) and height in meters (m), BMI is calculated as:
In plain language, the calculation divides kilograms by height in meters multiplied by itself.
Imperial BMI formula for pounds and inches
For a weight in pounds and height in inches, the BMI calculation is:
BMI = (weight in pounds ÷ (height in inches)²) × 703
The 703 factor puts the pounds-and-inches result on the same BMI scale as the metric calculation.
Adult BMI categories and comparison table
After calculating your BMI, this tool compares it with commonly used ranges for adults aged 18 and older:
| BMI range | Category | General interpretation |
|---|---|---|
| < 18.5 | Underweight | Body weight may be too low for most adults; can be linked with nutritional or health issues. |
| 18.5 – 24.9 | Healthy weight | Weight is generally associated with lower risk of many weight-related conditions. |
| 25.0 – 29.9 | Overweight | Higher likelihood of developing conditions such as type 2 diabetes or high blood pressure, especially with other risk factors. |
| 30.0 – 34.9 | Obesity class I | Increased health risks; medical and lifestyle review is usually recommended. |
| 35.0 – 39.9 | Obesity class II | Higher risk of serious health problems; professional guidance is strongly advised. |
| ≥ 40.0 | Obesity class III | Very high risk of obesity-related diseases; specialist medical support is typically appropriate. |
Adult BMI labels and cutoffs can vary slightly by guideline or country. The calculator applies widely referenced adult cutoffs for general information, not an individual clinical assessment.
How to use the adult BMI calculator
- Enter your current weight and select kilograms (kg) or pounds (lb).
- Enter your height in centimeters (cm) or inches (in). For feet and inches, first convert your height to total inches, or enter centimeters.
- Optionally enter a target weight in the same unit selected for your current weight. The result will include the BMI at that target weight and your current height.
- Optionally provide age, gender, and activity level. These fields produce BMR and estimated daily calorie figures; they do not change your BMI calculation.
- Select the calculate button to see your BMI, adult category, healthy-weight range for your height, and any optional energy estimates.
Re-entering a different weight at the same height is a straightforward way to see how the BMI value and category would change.
Worked example: BMI and target BMI at 1.75 m
Consider an adult who weighs 72 kg and is 1.75 m tall.
- Weight = 72 kg
- Height = 1.75 m
Using the metric BMI formula:
BMI = 72 ÷ (1.75 × 1.75) = 72 ÷ 3.0625 ≈ 23.5
A BMI of about 23.5 is within the calculator’s 18.5–24.9 adult healthy-weight range. If the same person used a target weight of 80 kg, their target BMI at 1.75 m would be:
BMI = 80 ÷ 3.0625 ≈ 26.1, which is in the overweight range. The example illustrates why BMI changes with weight when height remains fixed.
BMR and daily calorie estimates alongside BMI
When age, gender, and activity level are supplied, the BMI calculator also estimates basal metabolic rate and total daily energy expenditure.
- Basal Metabolic Rate (BMR) estimates calories used over 24 hours at rest to support essential functions such as breathing, circulation, and basic cellular processes.
- Total Daily Energy Expenditure (TDEE) multiplies the BMR estimate by the selected activity level to approximate calories used on a typical day.
For the calculator’s energy estimates:
- Calories near estimated TDEE may be consistent with maintaining weight over time.
- Consuming less than estimated TDEE over time may contribute to weight loss.
- Consuming more than estimated TDEE over time may contribute to weight gain.
BMR and TDEE are broad estimates rather than measured calorie requirements. A safe, sustainable weight-change approach depends on medical history, diet, activity, and other individual factors, so discuss significant changes with a healthcare professional or registered dietitian.
Interpreting an adult BMI result
An adult BMI category is one screening result, not a complete picture of health. Consider the following when reading your calculation:
- 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 need age- and sex-specific BMI percentile charts rather than these fixed adult ranges. This calculator is not designed for users under 18.
Beyond BMI: health indicators to consider with BMI
An adult BMI value cannot capture every aspect of health. The following measures can add useful context:
- 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.
Where possible, consider your BMI result together with these measures, your personal medical history, and your family history.
Adult BMI limitations, assumptions, and medical disclaimer
This adult BMI calculator is a screening tool with important limitations and 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 adult BMI, healthy-weight, and energy calculator
This calculator computes adult BMI from converted metric height and weight, then uses the 18.5–24.9 range to show a healthy-weight range for your height. A target-weight BMI uses the same selected weight unit as your current weight. When the optional age, gender, and activity fields are complete, it also calculates BMR with a commonly used predictive equation and estimates TDEE using the selected activity multiplier. These figures are approximate and can differ from clinical measurements or individualized advice.
| Classification | BMI |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 - 24.9 |
| Overweight | 25.0 - 29.9 |
| Obesity class I | 30.0 - 34.9 |
| Obesity class II | 35.0 - 39.9 |
| Obesity class III | ≥ 40.0 |
Balance Band Dash
Steer the energy pulse into the healthy BMI band and ride the rhythm of weight-to-height balance. Every catch teaches how small shifts move the needle.
Tap or drag to nudge. Keyboard: ← → to steer, space to stabilize, Esc to pause. Catch bonus orbs for calm focus boosts.
Play for 90 seconds by keeping the moving pulse within the healthy BMI band. Tap, drag, or use arrow keys to steer. Press space to steady the pulse and Escape to pause or resume.