BMI Calculator

Calculate your Body Mass Index (BMI) using metric or imperial measurements.

BMI Calculator

Enter your height and weight above to see your Body Mass Index score instantly.

How to Use

1

Select metric or imperial units

Choose kilograms/centimetres or pounds/feet-inches based on your available measurements.

2

Enter your height

Input height in cm (metric) or feet and inches (imperial) accurately.

3

Enter your body weight

Use your most recently measured weight for the most accurate BMI result.

4

Review BMI and weight category

See your BMI value and WHO category. Consult a doctor for a full health evaluation.

Understanding BMI

Body Mass Index (BMI) is a person's weight in kilograms divided by the square of height in meters. It is an inexpensive and easy screening method for weight category — underweight, healthy weight, overweight, and obesity.

Real-World Examples & Use Cases

Initial Adult Weight Screening

BMI is the standard first-step screening tool used in clinical settings to identify adults who may be at increased health risk from their weight. The WHO and national health agencies use BMI thresholds to categorize populations for public health monitoring. At the individual level, a first BMI calculation helps adults understand whether their weight falls within a healthy range and provides a starting reference point for conversations with healthcare providers about lifestyle, nutrition, and fitness goals.

Weight Loss and Fitness Goal Setting

People beginning a weight loss journey use BMI to set a concrete, measurable goal. If your current BMI is 29.4 (overweight) and your target is BMI 24.9 (upper Normal), you can calculate the exact weight loss in kilograms or pounds needed to cross the threshold. Tracking BMI monthly during a diet or exercise program provides objective feedback on progress. The change from one category to the next (e.g., Obese to Overweight) represents a meaningful health milestone regardless of the number on the scale.

Paediatric BMI Tracking (with percentile charts)

For children and teenagers, BMI is assessed differently than for adults — it is plotted against age- and sex-specific growth charts to produce a BMI-for-age percentile. A child at the 95th percentile or above is considered obese; 85th-94th percentile is overweight. Parents tracking their child's growth can calculate BMI at each annual health check to identify trends early. Paediatric BMI must always be interpreted by a paediatrician with age and sex context, not compared directly to adult categories.

Pre-Surgical and Insurance Health Assessments

BMI is widely used as a selection criterion for medical procedures and insurance risk assessment. Many elective surgical procedures (joint replacements, bariatric surgery eligibility assessment, organ transplant waitlisting) use BMI thresholds. Health insurers in some markets use BMI as a factor in risk classification. Life insurance underwriters request BMI as part of the medical questionnaire. Understanding your BMI before these assessments allows you to have informed conversations about what your number means in the specific context of the procedure or policy being evaluated.

How It Works

BMI Formula: Metric: BMI = Weight (kg) / Height (m)² Imperial: BMI = (Weight (lb) × 703) / Height (in)² Example: Person: 75 kg, 175 cm (1.75 m) BMI = 75 / (1.75)² = 75 / 3.0625 = 24.5 → Normal weight WHO Adult BMI Categories: < 18.5 → Underweight 18.5 – 24.9 → Normal weight 25.0 – 29.9 → Overweight 30.0 – 34.9 → Obesity Class I 35.0 – 39.9 → Obesity Class II ≥ 40.0 → Obesity Class III BMI Prime = BMI / 25 (ratio to upper Normal boundary) Limitation: BMI does not distinguish fat from muscle. Athletes, elderly persons with muscle loss, and people of different ethnic backgrounds may have different health risks at the same BMI. Asian populations show increased health risk at lower BMI thresholds (≥ 23 overweight, ≥ 27.5 obese).

Frequently Asked Questions

Is BMI an accurate measure of health?▼
BMI is a useful population-level screening tool but has significant limitations as an individual health measure. It does not distinguish between fat mass and lean muscle mass — a muscular athlete may have a high BMI while having very low body fat. It does not account for fat distribution (visceral abdominal fat poses higher health risks than subcutaneous fat). Age, sex, and ethnicity all affect healthy BMI ranges. BMI is best used as a starting point, not a definitive health assessment. Waist circumference and body fat percentage provide complementary information.
What BMI range is considered healthy for adults?▼
The WHO defines the healthy adult BMI range as 18.5 to 24.9. Below 18.5 is underweight (associated with malnutrition, immune issues, and bone density loss). 25.0–29.9 is overweight (modestly increased risk of cardiovascular disease and type 2 diabetes). 30 and above is obese (progressively higher risk of multiple chronic diseases). Some Asian health organizations use lower thresholds: overweight starts at 23, obesity at 27.5, reflecting population-specific research.
Does BMI apply to children the same way as adults?▼
No. For children and teens (ages 2-19), BMI is interpreted using age- and sex-specific percentile charts rather than fixed thresholds. Children grow rapidly and normally, so a 'healthy' BMI value changes with age and differs between boys and girls. A child's BMI is classified as: underweight (< 5th percentile), healthy (5th-84th), overweight (85th-94th), obese (≥ 95th). Always use paediatric BMI-for-age charts and consult a paediatrician for evaluation.
What is the difference between overweight and obese?▼
Overweight (BMI 25.0–29.9) indicates excess body weight that modestly increases health risks. Obesity (BMI ≥ 30) is further subdivided into three classes of increasing severity. The distinction matters clinically: obesity is associated with substantially higher risks of type 2 diabetes, cardiovascular disease, sleep apnoea, certain cancers, and joint problems compared to overweight. Medical treatment protocols (medications, surgery eligibility) typically use BMI ≥ 30 or ≥ 35 thresholds as clinical decision points.
How much would I need to weigh to be in the normal BMI range?▼
Rearrange the formula: Target Weight = 24.9 × Height (m)². For a person 175 cm tall: Normal weight upper limit = 24.9 × (1.75)² = 24.9 × 3.0625 = 76.3 kg. Lower limit: 18.5 × 3.0625 = 56.7 kg. So for this height, the healthy weight range is approximately 56.7 kg to 76.3 kg. This calculation tells you the specific number range to target rather than an abstract BMI figure.

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