BMI Calculator
Calculate your Body Mass Index in metric or imperial units. Get your category, healthy weight range, animated visual scale, and a personalised insight — instantly.
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese Class I |
| 35.0 – 39.9 | Obese Class II |
| 40.0 & above | Obese Class III |
How to calculate your BMI
Select Metric to enter your height in centimetres and weight in kilograms, or Imperial to enter feet, inches, and pounds. Your BMI updates in real time as you type — no button press needed.
The visual scale shows a pointer on a colour-coded bar (blue → green → amber → orange → red) indicating exactly where your BMI falls across the full range from 10 to 45.
Below the score you can see your healthy weight range for your current height, and how many kilograms or pounds you would need to gain or lose to reach the normal BMI range (18.5–24.9).
BMI formula
Metric: BMI = weight (kg) ÷ height² (m). For example, 70 kg and 175 cm → 70 ÷ (1.75²) = 22.9.
Imperial: BMI = (weight (lbs) × 703) ÷ height² (inches). For example, 154 lbs and 5′9″ (69 in) → (154 × 703) ÷ (69²) = 22.7.
The World Health Organisation (WHO) defines the standard BMI categories used by this calculator. These categories apply to adults aged 18 and over. Different reference ranges are used for children and teenagers.
BMI categories explained
Underweight (BMI < 18.5): May indicate insufficient nutrition or an underlying health condition. A healthcare professional can advise on healthy weight gain strategies.
Normal weight (18.5–24.9): Associated with the lowest risk of weight-related health conditions. Maintaining this range through balanced diet and regular exercise is beneficial.
Overweight (25–29.9): Slightly elevated risk for conditions such as type 2 diabetes and cardiovascular disease. Even modest weight loss (5–10%) can significantly improve health outcomes.
Obese Class I–III (30+): Associated with significantly increased risk for numerous health conditions. Professional medical guidance can provide effective, evidence-based support.
Features
- Metric and Imperial — switch between kg/cm and lbs/ft/in instantly
- Real-time BMI calculation — updates as you type
- Animated visual scale — colour-coded bar from underweight to obese III
- BMI category badge with colour coding for at-a-glance clarity
- Healthy weight range — personalised to your height
- Weight difference — how much to gain or lose to reach the normal range
- Personalised insight message for each BMI category
- 100% client-side — your data never leaves your browser
Frequently asked questions
What is BMI?
BMI (Body Mass Index) is a number calculated from your height and weight using the formula weight (kg) ÷ height² (m). It is widely used as a screening tool to identify potential weight-related health concerns for adults. A BMI of 18.5–24.9 is considered normal weight.
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above falls in the obese category. These thresholds are set by the World Health Organisation and apply to adults aged 18+.
Is BMI accurate for everyone?
BMI is a screening tool and has notable limitations. It does not account for muscle mass, bone density, fat distribution, age, or sex. Athletes and highly muscular individuals may have a high BMI that doesn't reflect excess body fat. Older adults may have a healthy BMI but still carry excess fat. Use BMI alongside other health assessments for a complete picture.
How do I use imperial units (feet and pounds)?
Click Imperial (lbs, ft) at the top. Enter your height in feet and inches in the two separate fields, and your weight in pounds. The formula used is BMI = (weight_lbs × 703) ÷ height_in², where height_in is your total height converted to inches.
How is the healthy weight range calculated?
The healthy weight range shows the weight that corresponds to a BMI of 18.5 (lower bound) and 24.9 (upper bound) for your entered height. Formula: min weight = 18.5 × height² (m), max weight = 24.9 × height² (m). For Imperial output, the result is converted to pounds.
Does this calculator work for children?
No — this calculator is designed for adults aged 18 and over. BMI interpretation for children and teenagers uses age- and sex-specific percentile charts, not the fixed adult thresholds. For children, consult a paediatrician or use a child-specific BMI tool.