BMI calculator
Quick body mass index check using height and weight.
Health
Health converters
Health and fitness calculators for BMI, ideal weight, calorie conversion and water intake. All calculations run in your browser, so no data is sent or stored. Results are reference values only, not medical advice.
Last updated: May 2026
Tools in this section
MG to ML calculator
Educational dose-volume calculator with a clear medical disclaimer.
Calorie to kJ
Convert food energy labels between calories and kilojoules.
Water intake calculator
Estimate a simple daily hydration target.
Ideal weight calculator
Rough reference weight range based on height.
These health and fitness tools turn numbers you already have, such as your height, weight, age or a food label, into a figure you can act on. Each one runs entirely in your browser, stores nothing, and shows a reference estimate rather than a diagnosis. For anything that affects medication, treatment or a medical condition, treat the result as a starting point and confirm it with a qualified professional.
What BMI categories mean in practice
BMI is calculated by dividing body weight in kilograms by height in metres squared. Because it uses only two measurements, it does not distinguish muscle from fat, which means a muscular athlete and a sedentary person of the same height and weight will score identically. Despite this limitation, BMI is widely used because it is fast, free and correlates with population-level health outcomes at scale.
| BMI range | WHO category | Practical note |
|---|---|---|
| Below 18.5 | Underweight | Associated with nutritional deficiency risk; individual variation is high |
| 18.5 to 24.9 | Healthy weight | Population average range; athletes may read higher due to muscle mass |
| 25.0 to 29.9 | Overweight | Elevated risk for metabolic conditions at population level |
| 30.0 to 34.9 | Obese class I | Risk increases with higher values; sub-categories continue at 35 and 40 |
For reference: a person 170 cm tall falls in the healthy range at 53 to 72 kg. At 180 cm the healthy range is 60 to 81 kg. The BMI calculator computes the score and shows which band it falls into.
Health metrics in everyday use
Water intake guidelines vary by body weight, activity and climate. The 30 to 35 ml per kilogram rule gives a baseline: an 80 kg adult in a temperate climate needs roughly 2.4 to 2.8 litres per day from all sources including food. During intense exercise or in heat that rises by 0.5 to 1 litre per hour of activity. The water intake calculator gives a starting figure based on your weight.
Food energy labels in Europe show both kcal and kJ. One kilocalorie (the "Calorie" on nutrition labels) equals 4.184 kJ. A typical adult maintenance intake is around 2000 to 2500 kcal per day, or 8370 to 10460 kJ. The calorie to kJ converter is useful when comparing products labelled in different units, or when reading nutrition research that uses kJ exclusively.
Medication dosing that involves mg-to-mL conversion depends on the concentration of the solution. If a liquid paracetamol has a concentration of 250 mg per 5 mL, a 500 mg dose requires 10 mL. The mg to mL calculator shows the calculation with a clear disclaimer that all dosing decisions must be confirmed with a qualified pharmacist or healthcare professional.
Frequently Asked Questions
Is BMI an accurate measure of health?
BMI is a quick screen based only on height and weight. It does not separate muscle from fat or account for age and build, so athletes and older adults can be misclassified. Use it as a rough indicator, not a diagnosis.
How much water should I drink a day?
A common guideline is roughly 30 to 35 ml per kilogram of body weight, adjusted for activity, heat and health. The water intake calculator gives a starting estimate, not a medical target.
How do I convert calories to kilojoules on a food label?
Multiply calories (kcal) by 4.184, so a 250 kcal snack is about 1046 kJ. EU labels usually show both numbers, and the calorie to kJ tool converts either way.
What is a healthy weight for my height?
The ideal weight calculator gives a reference range from height-based formulas. A healthy weight still varies with build and muscle mass, so use the range as guidance rather than a fixed target.
Are these tools medical advice?
No. Every result is an educational estimate calculated locally in your browser with nothing stored. For diagnosis, dosing or treatment decisions, consult a qualified healthcare professional.
What is the difference between BMI and body fat percentage?
BMI is calculated from height and weight only and does not measure fat directly. Body fat percentage requires a different method such as a DEXA scan, callipers or a bioimpedance scale. A muscular person can have a high BMI but a low body fat percentage. For most people the two correlate well enough for general screening purposes.
How do I read the kJ number on a food label?
Divide kJ by 4.184 to get kcal. A label showing 840 kJ per serving is 200 kcal. EU food labels show both numbers by law; US labels use kcal only. The calorie to kJ converter handles either direction.
What does mg per mL mean on a liquid medicine label?
It is the concentration: milligrams of active ingredient per millilitre of liquid. A 250 mg per 5 mL suspension has 50 mg/mL, so a 500 mg dose is 10 mL. Always check the concentration on the specific bottle before measuring, as the same medicine may come in different strengths.