BMI Calculator at a glance
- What it does
- Calculate body mass index from height and weight in metric or imperial units, with an honest explanation of what BMI does and does not measure.
- Where it runs
- Entirely in your browser — no data is uploaded
- Works offline
- Yes, once the page has loaded
- Cost
- Free, with no account and no usage limit
- Category
- General Calculators
How to use the calculator
- Choose metric or imperial units.
- Enter your height and weight.
- Read the BMI and its category, then read the limitations below before drawing any conclusion.
The formula
Metric: BMI = weight(kg) / height(m)²
Imperial: BMI = 703 × weight(lb) / height(in)²A person of 70 kg and 1.75 m has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.
| BMI | WHO category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 - 24.9 | Healthy weight |
| 25.0 - 29.9 | Overweight |
| 30.0 - 34.9 | Obesity class I |
| 35.0 - 39.9 | Obesity class II |
| 40.0 and above | Obesity class III |
What BMI cannot tell you
Adolphe Quetelet devised the formula in the 1830s as a way of describing populations. He explicitly said it was not a measure of individual fatness, and he was right.
- It cannot distinguish muscle from fat. Muscle is denser, so athletes routinely register as overweight or obese while carrying very little body fat.
- It ignores fat distribution. Visceral fat around the organs carries far more metabolic risk than subcutaneous fat, and BMI is blind to the difference. Waist circumference and waist-to-height ratio are better single indicators.
- It scales badly with height. Dividing by height squared under-reports for tall people and over-reports for short ones, because bodies do not scale as squares.
- The thresholds are not universal. Cardiometabolic risk rises at lower BMI in South Asian and East Asian populations, so several countries use lower cut-offs - around 23 for overweight.
- It does not apply to everyone. Children and adolescents need age and sex percentiles. It is not valid during pregnancy, and it loses accuracy in older adults as muscle mass declines.
Measures that tell you more
Waist-to-height ratio. Waist circumference divided by height; below 0.5 is the usual target. It requires one tape measure, applies across populations, and predicts metabolic risk better than BMI.
Waist circumference alone. Commonly cited thresholds are above 94 cm for men and 80 cm for women, with lower values for some ethnic groups.
Body composition. DEXA scanning is the reference standard; bioelectrical impedance scales are convenient but vary with hydration.
Actual health markers. Blood pressure, fasting glucose, HbA1c, lipid profile and cardiorespiratory fitness. These measure what you actually care about rather than a proxy for it, and someone can be metabolically healthy at a high BMI or unhealthy at a normal one.
Using the number sensibly
BMI is best treated as one crude screening input, most useful for tracking change in yourself over time rather than for comparison against other people. A BMI that has moved from 24 to 29 over three years is meaningful information about a trend; a single reading of 26 in isolation tells you very little.
If the number concerns you, a conversation with a doctor who can also check blood pressure, blood sugar and cholesterol will tell you something a formula from 1832 cannot.
This calculator is informational and is not medical advice. It cannot diagnose anything. Discuss health concerns with a qualified healthcare professional - see our disclaimer.
Frequently asked questions
It is accurate as arithmetic and limited as a health measure. It cannot distinguish muscle from fat or account for where fat is stored, so it misclassifies athletes, older adults and many people of normal weight with high visceral fat.
The WHO range is 18.5 to 24.9 for adults. Several Asian countries use lower thresholds because health risks appear at lower BMI in those populations.
Not in the adult form. Children are assessed against age-and-sex percentile charts, because healthy body composition changes throughout growth.
Waist-to-height ratio is a better single number and needs only a tape measure. Actual health markers - blood pressure, fasting glucose, lipids, fitness - are better still.
No. The calculation runs in your browser and nothing is recorded or transmitted.
Nothing you enter here leaves your browser
BMI Calculator does its work in JavaScript running on your own device. The page loads once, and after that there is no upload step and no server involved — which matters here because your figures are yours, and nobody needs a record of them.
You can verify this rather than taking our word for it: load the page, disconnect from the internet, and the tool keeps working. Our privacy policy sets out what is and is not collected, and this guide explains why the distinction matters.