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Macro Calculator
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BMI Calculator
Enter your height and weight (metric or imperial) to calculate your BMI and see where you fall on the standard BMI scale — underweight, normal, overweight, or obese.
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How to use the BMI Calculator
Choose metric or imperial
Use the toggle at the top to switch between metric (cm / kg) and imperial (ft + in / lbs). All inputs update instantly when you switch units.
Enter your height and weight
For metric, enter your height in centimetres and weight in kilograms. For imperial, enter height in feet and inches separately, and weight in pounds.
Read your BMI and category
Your BMI appears as a large number with a colour-coded category badge: blue for underweight, green for healthy weight, amber for overweight, and red for obese.
Check the BMI scale and healthy weight range
The visual BMI scale bar shows exactly where your BMI sits across all four zones. Below it, your healthy weight range for your height is shown in kg, lbs, and stones/pounds.
About this BMI Calculator
BMI (Body Mass Index) is a simple calculation that uses your height and weight to estimate whether you're in a healthy weight range. It's calculated by dividing your weight in kilograms by the square of your height in metres. Our free BMI calculator handles both metric and imperial inputs and gives you an instant result alongside the standard WHO classification. The four BMI categories are: Underweight (below 18.5), Healthy weight (18.5–24.9), Overweight (25–29.9), and Obese (30 and above). These thresholds were defined by the World Health Organization based on population-level health risk data. However, BMI has well-known limitations. It doesn't distinguish between fat and muscle mass, so a heavily muscled athlete may register as "overweight" despite having very low body fat. It also doesn't account for age, sex, or fat distribution — a key factor in cardiovascular risk. These are the reasons BMI is described as a screening tool, not a diagnostic test. Always interpret your BMI in the context of your overall health, and consult a healthcare professional for personalised guidance.
Frequently Asked Questions
According to the WHO, a BMI of 18.5–24.9 is considered normal/healthy weight. Under 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese. BMI is a screening tool, not a diagnostic measure.
BMI is a useful population-level screening tool but has limitations for individuals. It doesn't account for muscle mass, bone density, age, sex, or fat distribution. Athletes can have a high BMI despite low body fat. Use it alongside other health indicators.
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = (weight in lbs × 703) ÷ height (in)². For example, someone 5'9" (175 cm) weighing 160 lbs (73 kg) has a BMI of roughly 23.6.
BMI doesn't distinguish between muscle and fat, so a muscular athlete can have a 'high' BMI despite low body fat. It also ignores bone density, age, sex, fat distribution (visceral vs subcutaneous), and ethnicity. Researchers have found that people of Asian descent face higher health risks at lower BMI thresholds, which is why some guidelines use adjusted categories for different ethnic groups.
Yes. For children and teenagers (ages 2–19), BMI is interpreted using age- and sex-specific percentile charts, not fixed thresholds. A BMI that's normal for a 7-year-old boy is different from what's normal for a 15-year-old girl. Our calculator is designed for adults aged 18 and over.
The standard BMI thresholds (18.5–24.9 for healthy weight) are the same for men and women. However, because women naturally carry more body fat than men at the same BMI, some researchers argue the thresholds should differ by sex. For everyday use, the same 18.5–24.9 range is applied regardless of gender.