BMI Calculator
Enter your height and weight below to find your Body Mass Index, see which weight category it falls into, and check the healthy weight range for your height.
Calculate your BMI
Please enter a valid height and weight.
How this BMI calculator works
Body Mass Index is calculated from just two numbers: your height and your weight. First, the calculator divides your weight by the square of your height, then checks the result against the World Health Organization's adult weight categories. As a result, metric and imperial units give the same result — the calculator just uses a different version of the formula for each.
The formula, if you're curious
Metric: BMI = weight (kg) ÷ height (m)². For example, someone who is 1.70 m tall and weighs 68 kg has a BMI of 68 ÷ (1.70 × 1.70) = 23.5.
Imperial: BMI = 703 × weight (lb) ÷ height (in)². Someone who is 5'7" (67 inches) and weighs 150 lb has a BMI of 703 × 150 ÷ (67 × 67) = 23.5 — the same result, just in different units.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 16.0 | Severe thinness |
| 16.0 – 16.9 | Moderate thinness |
| 17.0 – 18.4 | Mild thinness |
| 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 and above | Obese Class III |
These ranges apply to adults aged 20 and over and are the same for men and women. They come from World Health Organization guidance and are widely used by health organizations worldwide. The calculator above groups results into the four broad categories for simplicity, but the finer breakdown here is useful if your result sits near a boundary.
What your healthy weight range means
In addition to your BMI, the calculator shows a healthy weight range for your exact height — the span of weights that would put you in the "normal" category. This is often more useful day-to-day than the BMI number itself, because it tells you directly how many kilograms or pounds separate you from that range, rather than requiring you to do the math yourself.
Health risks linked to being overweight
According to the CDC, carrying excess weight over time is associated with a higher risk of several conditions, including:
- High blood pressure and unfavorable cholesterol levels
- Type 2 diabetes
- Coronary heart disease and stroke
- Osteoarthritis and joint strain
- Sleep apnea and breathing difficulties
- Certain cancers, including breast, colon, and kidney
Therefore, most public health guidance suggests aiming to keep BMI under 25 where possible, though the right target for any individual is best worked out with a doctor rather than a calculator alone.
Health risks linked to being underweight
On the other hand, being underweight carries its own risks, which are sometimes overlooked:
- Nutrient deficiencies and anemia
- Weakened bone density and higher fracture risk
- Reduced immune function
- Fertility and hormonal effects
A low BMI can also be a sign of an underlying condition, so it's worth discussing with a doctor rather than assuming it's automatically healthy.
Limitations of BMI
Overall, BMI is a fast screening tool, not a full health assessment. Specifically, it doesn't account for:
- Muscle mass — muscle is denser than fat, so muscular people can register as "overweight" despite low body fat.
- Body fat distribution — BMI can't tell visceral fat (around organs) from fat elsewhere, even though location matters for health risk.
- Age and bone density — older adults can have a "normal" BMI while carrying less muscle and more fat than the number suggests.
If you want a fuller picture, pairing your BMI with a body fat percentage or waist measurement gives more context than either number alone.
What is BMI Prime?
BMI Prime is your BMI divided by 25 — the upper edge of the "normal" range. It's a quick way to see how close you are to that boundary regardless of units: a BMI Prime of 1.0 means you're sitting exactly at the top of the normal range, below 1.0 means you're under it, and above 1.0 tells you how far over it you are. It's the same information as your BMI, just rescaled to make comparisons easier.
Tips for maintaining a healthy weight
- Eat a balanced diet built around whole foods — vegetables, fruit, lean protein, and whole grains.
- Move regularly — aim for at least 150 minutes of moderate activity a week, spread across several days.
- Prioritize sleep — poor sleep is linked to changes in appetite hormones and metabolism.
- Track trends, not single days — weight fluctuates daily from water and food volume; look at the direction over weeks, not one reading.
Frequently asked questions
Is BMI accurate for everyone?
BMI is a screening tool, not a diagnosis. It doesn't distinguish muscle from fat, so it can overestimate body fat in athletes and underestimate it in older adults with reduced muscle mass. It's best used as a starting point, alongside other measurements.
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 falls in the "normal weight" range set by the World Health Organization. This range is the same for men and women, though individual health depends on more than BMI alone.
Does this BMI calculator work for children?
No. This calculator uses adult BMI thresholds. Children and teens need age- and sex-specific percentile charts, which a pediatrician can provide.
How often should I check my BMI?
Every few months is enough for most people tracking gradual changes. Daily or weekly checks usually just reflect normal water-weight fluctuation, not real changes in body composition.
Why do two people with the same BMI look different?
BMI only uses height and weight, so it can't tell the difference between muscle, fat, and bone. Two people at the same BMI can have very different body compositions, which is why BMI works best alongside a body fat or waist measurement.
Is BMI different for men and women?
The BMI formula and the standard category ranges are the same for adult men and women. What differs is body composition at a given BMI — women naturally carry a higher percentage of body fat than men at the same BMI, which is one reason BMI is treated as a starting point rather than the full picture.
What's a good BMI for someone over 50?
The standard 18.5–24.9 "normal" range still applies, but some research suggests a slightly higher BMI (up to around 27) may carry less risk for older adults, partly because a bit of extra reserve can help during illness. This is an area where individual guidance from a doctor matters more than a general calculator.
This calculator provides general information and isn't a substitute for medical advice. If you have concerns about your weight or health, talk with a doctor or registered dietitian.