ReckonBoxHow this BMI calculator works
Body mass index is your weight in kilograms divided by your height in metres squared. It is a fast screen for whether your weight sits in a healthy range for your height. It is not a measure of body fat, and it does not know how much of you is muscle. This tool computes it in metric or imperial units, classifies it with the WHO standard or Asian cutoffs, and shows the healthy weight range for your height. Everything runs in your browser, so the numbers you type never leave your device.
The formula is the same idea in both unit systems:
- Metric:
BMI = weight (kg) / height (m)^2 - Imperial:
BMI = 703 x weight (lb) / height (in)^2
Here is a worked one. Someone 5 ft 10 in (1.78 m) at 160 lb (72.6 kg) has a height squared of 3.16, so their BMI is 72.6 / 3.16, about 23.0. That sits in the WHO normal range, and their healthy weight for that height runs from roughly 129 to 174 lb. The top of that range is also the answer to a common question: to reach a normal BMI, aim for a weight at or below the upper number.
BMI categories
BMI bands sort the number into weight categories. The WHO standard applies worldwide. The Asian cutoffs shift the lines down, because health risks climb at a lower BMI for many South and East Asian people. This tool re-classifies your result when you pick the Asian standard, rather than just mentioning the thresholds.
| Category | WHO standard | Asian cutoffs |
|---|---|---|
| Underweight | below 18.5 | below 18.5 |
| Normal weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25 to 29.9 | 23 to 27.4 |
| Obesity | 30 and above | 27.5 and above |
Is BMI different for men, women, age, and ethnicity?
The BMI formula does not change for men and women, and adult BMI does not adjust for age. A 30 year old man and a 30 year old woman with the same height and weight get the same BMI. What differs is how to read it. Women carry more essential fat on average, and older adults lose muscle, so the same BMI can mean different things for body composition.
Two groups deserve a second look at the verdict. Adults over about 65 may be better off at a slightly higher BMI, roughly 25 to 27, where a little reserve helps. And BMI tends to overestimate risk in Black adults and underestimate it in adults of Asian descent, which is why the Asian cutoffs exist. Children and teens are the real exception: for ages 2 to 19, BMI is read against age and sex percentiles, so a dedicated child and teen tool gives the right number.
Healthy weight for your height
The calculator turns your BMI band back into a weight. It multiplies the healthy BMI limits by your height squared, so you see the actual pounds or kilograms that keep you in range. Under the WHO standard that spans BMI 18.5 to 24.9. Under the Asian cutoffs the upper limit drops to 23.
When BMI misleads
BMI is a screen, not a diagnosis, and it misreads several groups:
- Muscular athletes can land in the overweight or obese band while carrying low body fat.
- Older adults may show a normal BMI while having lost muscle and gained fat.
- During pregnancy, BMI does not apply in the usual way.
- It says nothing about where fat sits, and belly fat carries more risk. A waist measurement adds the context BMI misses.
Health risks linked to high and low BMI
A high BMI raises the odds of type 2 diabetes, high blood pressure, heart disease, and several cancers. A very low BMI brings its own problems: weakened immunity, bone loss, and fertility trouble. BMI is one signal among many, so read it next to your blood pressure, blood sugar, waist size, and a conversation with a clinician.
Frequently asked questions
Is BMI different for men and women? No. The formula is the same for men and women. Body composition differs on average, so read BMI alongside other measures.
What is a healthy BMI? Under the WHO standard a BMI from 18.5 to 24.9 is the healthy range. The Asian cutoffs set the upper limit at 23.
Why offer Asian BMI cutoffs? Health risks rise at a lower BMI for many South and East Asian people, so the WHO suggests 23 for overweight and 27.5 for obesity.
This tool is an estimate, not medical advice. For decisions about your weight or health, talk to a doctor or a registered dietitian.