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Work out your Body Mass Index (BMI) from your height and weight, in either metric or imperial units, and see which weight category it falls into. You can also work backwards to find the healthy weight range for your height.
How to use the BMI Calculator
Choose metric or imperial units, then enter your height and weight to see your BMI and weight category. Switch to "Healthy weight range" to see the weight range that corresponds to a normal BMI at your height, without needing to enter a weight.
What is BMI?
Body Mass Index (BMI) is a simple ratio of weight to height, used worldwide as a quick screening tool for weight-related health risk. It doesn't measure body fat directly, and it doesn't account for muscle mass, body shape, age or sex, so it works best as a general population-level guide rather than a precise individual health assessment.
BMI formula
- Metric: BMI = weight (kg) ÷ height (m)²
- Imperial: BMI = 703 × weight (lb) ÷ height (in)²
For example, someone who is 175 cm tall and weighs 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the normal weight range.
BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
These are the standard adult ranges used by health bodies such as the World Health Organization. They apply to adults aged 20 and over, not to children or teenagers, whose healthy BMI depends on age and sex. Some countries and health bodies use lower thresholds; for example, several health authorities in parts of Asia classify a BMI of 23 or above as overweight, reflecting research that health risk can rise at a lower BMI in some populations.
How to find your healthy weight range
Rather than calculating BMI from a weight you already have, the "Healthy weight range" mode rearranges the same formula to solve for weight, using the lower and upper bounds of the normal range (18.5 and 24.9). This gives the weight range that would put someone of a given height into the normal BMI category.
Limitations of BMI
BMI does not distinguish between muscle and fat, so very muscular people can show a high BMI without excess body fat, and it may under- or overestimate health risk for some ethnic groups, older adults, and people of unusually short or tall stature. It is best used as one general indicator alongside other measures, not as a standalone diagnosis. If you have concerns about your weight or health, talk to a doctor or qualified health professional.
Real-world uses
- Getting a quick, general sense of whether your weight falls in a typical healthy range for your height.
- Tracking BMI over time alongside other health measures.
- Working out a general target weight range before setting a personal health goal, ideally with professional guidance.
- Understanding the weight categories used in health screening and research.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is classed as normal weight. This range is a general guide and can vary by population and individual circumstances.
How is BMI calculated?
In metric units, divide weight in kilograms by height in metres squared. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared.
Is BMI accurate for everyone?
No. BMI is a useful population-level screening tool, but it doesn't account for muscle mass, body fat distribution, age, sex or ethnicity, so it can be misleading for very muscular people, older adults, and some ethnic groups.
Does BMI apply to children?
No, not in the same way. Children and teenagers are assessed using BMI-for-age percentiles specific to their age and sex, not the fixed adult categories used here.
What is a healthy weight for my height?
Use the "Healthy weight range" mode to see the weight range that corresponds to a normal BMI (18.5–24.9) at your height.
Why do some countries use different BMI cutoffs?
Research has found that health risk can increase at a lower BMI in some populations, so some health authorities, particularly in parts of Asia, use a lower threshold (such as 23) for classifying overweight.
Can BMI tell me my body fat percentage?
No. BMI is a ratio of weight to height, not a direct measurement of body fat. Two people with the same BMI can have very different amounts of muscle and fat.
Should I use metric or imperial units?
Either works, since the calculator converts the same underlying formula for both. Use whichever units you're most comfortable measuring in.