Your Body Metrics
About These Calculations
Body Mass Index (BMI)
BMI = weight (kg) ÷ height² (m²). Categories: Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥30. Source: World Health Organisation (WHO).
Basal Metabolic Rate (BMR) — Mifflin-St Jeor
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161. This is the gold-standard equation validated in multiple independent clinical studies.
Total Daily Energy Expenditure (TDEE)
TDEE = BMR × Activity Factor. Your TDEE represents the total calories you burn daily including all physical activity. It is the most useful figure for setting a caloric intake target aligned with your health goals.
How to Use This BMI Calculator
Enter your age, select the sex used by the Mifflin-St Jeor equation, and provide your weight in kilograms and height in centimetres. Choose the activity level that best describes your usual week rather than an unusually active or inactive day. After you submit the form, the calculator shows BMI, estimated BMR, TDEE, and example calorie targets. If you normally use pounds and inches, convert them before entering your measurements: 1 inch equals 2.54 centimetres and 1 pound equals about 0.454 kilograms.
Example: Understanding a Result
A person who is 175 cm tall and weighs 70 kg has a BMI of about 22.9, calculated as 70 ÷ 1.75². That number falls within the adult “normal” reference range, but it does not describe muscle mass, bone density, body-fat distribution, or overall fitness. The BMR estimate represents energy used at rest, while TDEE adds an activity estimate. Treat the calorie targets as a starting point and adjust gradually using real changes in weight, energy, and professional guidance.
Important Limitations
BMI is a population-level screening measure, not a diagnosis. It can misclassify athletes with high muscle mass, older adults, pregnant people, and some children. BMR and TDEE are estimates because metabolism, body composition, sleep, medication, and daily movement vary from person to person. Do not use the calculator to set an extreme diet or to replace advice from a doctor, registered dietitian, or other qualified health professional.
Using Your Results Responsibly
For a more useful comparison, take measurements under similar conditions and focus on trends over several weeks instead of reacting to one result. Weight can change because of hydration, food, clothing, and the time of day. If your goal is weight loss, a modest and sustainable calorie change is generally more practical than a severe restriction. Pair the numbers with sleep, strength, energy, blood pressure, and other health indicators. People with a medical condition, a history of disordered eating, or a rapidly changing weight should discuss goals with a qualified health professional.
Metric Differences Across People
Two people with the same BMI can have very different muscle, fat, and fitness levels. Likewise, two people with the same weight may have different energy needs because of height, age, body composition, activity, and health status. Use these metrics as conversation starters and planning estimates, not as labels or a score of personal worth. For children and teenagers, adult BMI categories are not appropriate; age- and sex-specific growth charts should be interpreted by a clinician.
BMI, BMR and TDEE Questions
Is BMI the same as body fat percentage?
No. BMI uses height and weight only. Body-fat percentage requires a different measurement method and can also have an error range.
Why does my TDEE change when I select another activity level?
TDEE multiplies estimated BMR by an activity factor. More movement generally increases the estimated calories needed to maintain body weight.
How often should I recalculate?
Recalculate after a meaningful change in weight or routine, rather than several times a day. Use the result together with longer-term trends and professional advice.