BMI Calculator | Calculate BMI, Check Ideal Weight, Daily Calories
BMI Calculator
Body Mass Index
More than just a number. Get your complete BMI analysis with interactive charts, ideal weight formulas, calorie needs, and personalised health insights.
Enter your details and press Calculate BMI
Visualise Your Data
Interactive BMI Charts
Three Clinical Methods
Ideal Weight Calculator
These are general estimates for adults taller than 5 feet (152 cm). Individual body composition and medical history should also be considered.
BMR & TDEE
Calorie Needs Calculator
Select your activity level to calculate your Total Daily Energy Expenditure (TDEE):
Calculated via the Mifflin-St Jeor equation — the most accurate BMR formula for most adults.
Understanding BMI
What Is Body Mass Index (BMI)?
Body Mass Index (BMI) is a numerical value derived from a person’s weight and height. First developed by Belgian mathematician Adolphe Quetelet in the 1830s and popularised by Ancel Keys in 1972, BMI is today the most widely used screening tool for categorising body weight relative to height. Our free BMI calculator computes this value instantly and contextualises the result with interactive charts and health analysis.
The BMI formula is straightforward: BMI = weight (kg) ÷ height² (m). In imperial units: BMI = 703 × weight (lb) ÷ height² (in). The result is a dimensionless score that places a person in one of four WHO-defined categories.
Limitations of BMI
While BMI is a practical population-level screening tool, it has recognised limitations for individuals. It cannot distinguish between lean muscle mass and fat mass — a muscular athlete may register as “Overweight” despite very low body fat. It also ignores fat distribution: visceral fat (around the abdomen) carries far higher health risks than subcutaneous fat, yet BMI cannot differentiate between them. Always use BMI alongside waist circumference, body fat percentage, and clinical assessment.
BMI for Children vs Adults
For adults aged 20 and over, the standard four-category BMI scale applies equally to men and women. For children and teenagers aged 2–19, BMI is calculated using the same formula but interpreted using age- and sex-specific percentile charts, because body composition changes significantly during development. Our BMI calculator focuses on adult measurements only.
Quick Reference
BMI by Height & Weight — Reference Table
The table below shows the weight thresholds for each BMI category across common adult heights. Use it as a quick reference alongside our interactive BMI calculator.
| Height | Underweight (<18.5) | Normal (18.5–24.9) | Overweight (25–29.9) | Obese (≥30) |
|---|---|---|---|---|
| 150 cm (4’11”) | < 41.6 kg | 41.6 – 56.1 kg | 56.3 – 67.3 kg | > 67.5 kg |
| 155 cm (5’1″) | < 44.4 kg | 44.4 – 59.9 kg | 60.1 – 71.8 kg | > 72.1 kg |
| 160 cm (5’3″) | < 47.4 kg | 47.4 – 63.7 kg | 64.0 – 76.5 kg | > 76.8 kg |
| 165 cm (5’5″) | < 50.3 kg | 50.3 – 67.7 kg | 68.1 – 81.4 kg | > 81.7 kg |
| 170 cm (5’7″) | < 53.5 kg | 53.5 – 71.9 kg | 72.3 – 86.5 kg | > 86.7 kg |
| 175 cm (5’9″) | < 56.7 kg | 56.7 – 76.3 kg | 76.6 – 91.7 kg | > 91.9 kg |
| 180 cm (5’11”) | < 59.9 kg | 59.9 – 80.7 kg | 81.1 – 97.1 kg | > 97.2 kg |
| 185 cm (6’1″) | < 63.3 kg | 63.3 – 85.2 kg | 85.6 – 102.7 kg | > 102.7 kg |
| 190 cm (6’3″) | < 66.7 kg | 66.7 – 89.8 kg | 90.3 – 108.2 kg | > 108.4 kg |
Evidence-Based Guidance
How to Improve Your BMI & Health
Whether your BMI calculator result is above or below the healthy range, the following strategies are backed by clinical evidence and can help you reach or maintain a healthier weight.
A daily deficit of ~500 kcal produces roughly 0.5 kg of fat loss per week — a rate considered safe by most clinical guidelines. Avoid extreme deficits that cause muscle loss and metabolic slowdown.
Protein increases satiety, preserves lean muscle during weight loss, and has a higher thermic effect than carbs or fat. Aim for 1.6–2.2 g per kg of bodyweight during active weight loss phases.
Building muscle raises your resting metabolic rate, making it easier to maintain a calorie deficit. Aim for 2–3 resistance sessions per week alongside regular cardiovascular activity.
Poor sleep elevates ghrelin (hunger hormone) and suppresses leptin (satiety hormone), making weight management significantly harder. 7–9 hours of quality sleep per night is a non-negotiable foundation.
Got Questions?
Frequently Asked Questions About the BMI Calculator
For adults aged 20 and older, a healthy BMI is 18.5 to 24.9. Below 18.5 is Underweight, 25–29.9 is Overweight, and 30 or above is Obese. These thresholds are identical for men and women under the standard WHO classification used by our BMI calculator.
BMI = weight in kilograms ÷ height in metres squared. For example, someone weighing 70 kg at 1.75 m has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In imperial units: BMI = 703 × weight (lbs) ÷ height² (inches). Our BMI calculator applies the correct formula automatically.
BMI is a useful screening tool at the population level but has limitations for individuals. It cannot distinguish fat from muscle, and does not account for fat distribution, ethnicity, age, or bone density. A heavily muscular person may have a high BMI without excess fat. Use BMI alongside waist circumference, body fat percentage, and clinical evaluation for a complete picture.
The standard BMI formula and category thresholds are identical for both sexes. However, women naturally carry a higher proportion of body fat than men at the same BMI — meaning BMI may slightly underestimate health risk in women and overestimate it in muscular men.
The WHO subdivides obesity into three classes: Class I (BMI 30–34.9), Class II (35–39.9), and Class III/severe obesity (≥40). Each class carries progressively higher risks of cardiovascular disease, type 2 diabetes, sleep apnoea, and certain cancers.
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to sustain basic physiological functions. While BMI uses only height and weight, BMR also accounts for age and sex. A higher BMI often correlates with a higher absolute BMR, but muscle mass is a more significant driver. Multiply BMR by an activity factor to get TDEE (Total Daily Energy Expenditure).
A safe rate of BMI reduction comes from losing roughly 0.5–1 kg per week through a moderate calorie deficit (–500 kcal/day) combined with resistance training and adequate protein intake. Avoid crash diets — they cause muscle loss, slow your metabolism, and typically result in weight regain. Always consult a healthcare professional before beginning a weight loss programme.
Our BMI calculator automatically shows three ideal weight estimates based on your height: the Devine, Robinson, and Miller formulas. For a rough guide, a healthy BMI of 18.5–24.9 corresponds to a specific weight range for each height — shown in the reference table above. At 170 cm, for example, the healthy weight range is approximately 53.5–71.9 kg.
This BMI calculator is designed for adults aged 20 and over. For children and teenagers (2–19 years), BMI must be interpreted using age- and sex-specific percentile charts because body composition changes substantially during development. Consult your paediatrician for child BMI assessment.
Yes — completely free, with no registration required. All calculations run entirely in your browser using client-side JavaScript. No personal data is transmitted to any server or stored anywhere. Your height, weight, and age never leave your device.