Calculate your Body Mass Index (BMI) instantly. Free online BMI calculator with ideal weight range and health insights.
| Category | BMI Range | Health Risk |
|---|---|---|
| Severely Underweight | < 16 | High |
| Underweight | 16 – 18.5 | Moderate |
| Normal Weight | 18.5 – 25 | Low |
| Overweight | 25 – 30 | Moderate |
| Obese Class I | 30 – 35 | High |
| Obese Class II | 35 – 40 | Very High |
| Obese Class III | > 40 | Extremely High |
BMI is a screening tool, not a diagnostic measure. Consult a healthcare professional for personalized health advice.
The Body Mass Index (BMI) Calculator is a free online tool that estimates your body fat level based on your height and weight. BMI is used worldwide by healthcare professionals as a quick screening measure to categorise individuals into weight status groups — underweight, normal weight, overweight, and obese. While BMI does not directly measure body fat percentage or account for muscle mass, it provides a reliable population-level indicator of weight-related health risks including cardiovascular disease, type 2 diabetes, and certain cancers. Use this calculator alongside other health metrics for a complete picture of your wellbeing.
Select your preferred unit system — metric (kg/cm) or imperial (lbs/ft+in) — using the toggle at the top of the calculator.
Enter your height accurately. For imperial, enter feet and inches separately. Remove shoes when measuring for the most accurate result.
Enter your current weight. Weigh yourself in the morning before eating for the most consistent readings.
Select your age and gender. These factors affect the interpretation of your BMI result and the ideal weight calculation.
Your BMI score, weight category, and healthy weight range appear instantly. The colour-coded gauge shows where you fall on the scale.
Use the BMI Classification Table below the calculator to understand the health risks associated with each category.
Body Mass Index is calculated by dividing your weight in kilograms by the square of your height in metres (kg/m²). The formula was developed by Belgian mathematician Adolphe Quetelet in 1832 as a statistical tool to study populations — not as a medical diagnostic instrument for individuals. Despite this origin, it became the standard clinical screening tool because of its simplicity and strong correlation with population-level health outcomes.
BMI has important limitations. It cannot distinguish between fat mass and lean muscle mass, which means a muscular athlete may have an 'overweight' BMI despite having very low body fat. Conversely, a person with a 'normal' BMI may have high visceral fat (fat around internal organs) which carries significant health risks. BMI also does not account for age, sex, or ethnicity — factors that affect the relationship between BMI and body fat.
For a more complete assessment, healthcare professionals use BMI alongside waist circumference, waist-to-hip ratio, body fat percentage measurements, and blood markers such as cholesterol and blood glucose. If your BMI is outside the normal range, use it as a prompt to speak with your doctor rather than a cause for alarm.
If your BMI is above the healthy range, the most effective approach combines a moderate calorie deficit with regular physical activity. Research consistently shows that a deficit of 500 calories per day produces approximately 0.5 kg of weight loss per week — a rate that is sustainable and preserves muscle mass better than aggressive restriction.
Strength training is particularly important during weight loss. It preserves lean muscle mass, which keeps your metabolic rate higher and improves body composition even when the scale doesn't move. Aim for 2–3 resistance training sessions per week alongside 150 minutes of moderate aerobic activity (the WHO recommendation).
Diet quality matters as much as quantity. A diet rich in protein (1.6–2.2g per kg of body weight), vegetables, whole grains, and healthy fats supports satiety, muscle retention, and metabolic health. The Pipstario Fitness Planner includes a 12-week structured programme combining these evidence-based principles into a day-by-day action plan.
Always weigh yourself at the same time of day (morning, before eating) and on the same surface. Body weight fluctuates by 1–3 kg throughout the day due to food, water, and activity.
A waist circumference above 94cm (men) or 80cm (women) indicates excess visceral fat even at a normal BMI. Measure at the midpoint between your lowest rib and hip bone.
If you strength train regularly, your BMI may overestimate body fat. In this case, use body fat percentage (measured by DEXA scan or bioelectrical impedance) as a more accurate metric.
The goal is not just to lower the number on the scale but to reduce fat mass while preserving or building muscle. A body recomposition approach achieves this better than calorie restriction alone.
A single BMI reading is less meaningful than the trend over weeks and months. Track your BMI monthly alongside energy levels, fitness performance, and blood markers for a complete picture.
If your BMI is outside the normal range, book a health check with your GP. They can order blood tests, assess cardiovascular risk, and provide personalised advice based on your full health picture.