BMI Calculator
Calculate your Body Mass Index with metric or imperial units.
Includes healthy weight range, body fat estimate, and TDEE.
100% private — all calculations run in your browser.
BMI Calculator
Understanding BMI — What It Measures and Its Limitations
Body Mass Index (BMI) is a simple numerical measure derived from your height and weight that has been used by health professionals worldwide for decades. It provides a quick baseline for weight categorization and is the starting point for most population-level health assessments. However, BMI has important limitations — it does not differentiate between muscle and fat mass, does not account for fat distribution (where fat is stored matters), and may misclassify athletes with high muscle mass as overweight or elderly individuals with low muscle as normal weight. This calculator presents BMI alongside supplementary estimates — body fat percentage (Deurenberg formula) and TDEE (Mifflin-St Jeor) — to give you a more complete picture alongside your BMI reading.
BMI Categories Explained
The World Health Organization defines four primary BMI categories for adults: Underweight (below 18.5) — may indicate inadequate nutrition, malabsorption, or other health concerns. Normal weight (18.5–24.9) — associated with the lowest risk of weight-related health issues. Overweight (25–29.9) — indicates excess weight that may increase risk of certain chronic conditions. Obese (30 and above) — further subdivided into Class I (30–34.9), Class II (35–39.9), and Class III (40+) based on severity. Some countries and ethnic groups use different cutoff points — for example, Asian populations may apply a lower obesity threshold of 27.5.
How to Use BMI Alongside Other Health Metrics
For a comprehensive health assessment, consider combining your BMI result with waist circumference (abdominal fat is a stronger predictor of cardiovascular risk than overall weight), body fat percentage (estimated using skinfold measurements, DEXA, or bioelectrical impedance), and blood pressure and lipid panel data from your healthcare provider. This calculator includes a Deurenberg body fat estimate and a Mifflin-St Jeor TDEE calculation with a light-activity multiplier to help you understand your energy balance alongside your weight status.
Privacy and Accuracy
All calculations run entirely in your browser. Your height, weight, age, and waist measurements are never uploaded, stored, or transmitted. The BMI formula and supporting calculations use established mathematical models — the standard WHO BMI formula, the Deurenberg body fat approximation, and the Mifflin-St Jeor basal metabolic rate equation. These are general estimates and not substitutes for professional medical assessment.
ToolsMatic BMI Calculator vs Alternatives
BMI Calculator — Frequently Asked Questions
What is BMI and how is it calculated?
BMI (Body Mass Index) equals your weight in kilograms divided by your height in meters squared (kg/m²). The calculator automatically converts imperial inputs (pounds, inches) to metric before computing. It is a standard population-level screening tool for weight categories.
What are the BMI categories and what do they mean?
Below 18.5: Underweight — may indicate nutritional concerns. 18.5–24.9: Normal weight — associated with lowest health risk. 25–29.9: Overweight — may increase risk of certain chronic conditions. 30 and above: Obese — further classified as Class I (30–34.9), Class II (35–39.9), and Class III (40+).
Is BMI accurate for athletes and muscular people?
BMI can overestimate body fat in athletes because muscle is denser than fat. A muscular person may have a BMI in the "overweight" range while having very low body fat. For athletes, body fat percentage measurements (DEXA, bioelectrical impedance) are more informative than BMI alone.
What is a healthy weight range?
A healthy weight corresponds to a BMI between 18.5 and 24.9. The calculator shows this as an actual weight range in both kilograms and pounds specifically calculated for your height — much more useful than a generic BMI number.
What is TDEE and how is it calculated here?
Total Daily Energy Expenditure (TDEE) estimates how many calories your body burns per day. This calculator uses the Mifflin-St Jeor BMR equation combined with a light activity multiplier (1.375). It is a general estimate — actual TDEE varies with your real activity level and metabolic factors.
Is my health data private?
Yes. All calculations run in your browser. Your height, weight, age, and waist measurements are never uploaded to any server, stored in any database, or transmitted anywhere. This is a fully client-side tool.
Should I use BMI as the only health metric?
No. BMI is a useful screening tool but has significant limitations. It should be interpreted alongside waist circumference, body fat percentage, blood pressure, and clinical assessment by a healthcare professional for a complete health picture.
How do I switch between metric and imperial?
Select the desired unit system from the Units dropdown. The calculator automatically converts your current height and weight values when you switch, so you do not need to re-enter them.