BMI Calculator

Enter a height and a weight and get a Body Mass Index figure, the band it falls into, and the weight range that would put you inside the normal band. All three come from the standard formula, calculated in the page rather than on a server.

Important: Not Medical Advice

This page is an educational calculator, not a medical device, and it does not diagnose, treat or prevent any condition. Its output is a general estimate built from average population figures; it ignores individual factors such as age, body composition, pregnancy, medication and medical history. Always speak to a qualified clinician about your own situation before acting on any number shown here.

What the Number Measures, and What It Does Not

Body Mass Index is a single ratio — weight divided by the square of height — invented as a way to compare populations, not individuals. It has survived because it needs two numbers that anyone can supply without equipment, and because the bands it produces correlate well enough with health outcomes across large groups. What it does not do is distinguish between the components of that weight. Muscle, fat, bone and fluid all count the same, which is the source of nearly every criticism of it and the reason it should be read alongside other measurements rather than instead of them.

• The page accepts either system. Switch the unit selector to Metric and you enter centimetres and kilograms; switch to Imperial and you enter inches and pounds.
• The metric calculation divides weight in kilograms by height in metres squared. The imperial calculation multiplies weight in pounds by 703 and divides by height in inches squared — the same relationship with a conversion constant folded in.
• The result is rounded to one decimal place, which is the precision the bands are designed around and more precision than the inputs justify.
• Alongside the figure, the page returns the band name, a one-line risk description for that band, and the weight range corresponding to a BMI of 18.5 to 24.9 at your height.

Entering Height and Weight in Either System

1. Pick Metric or Imperial first. The unit selector does not convert values you have already typed, so switching after entering numbers will change what those numbers mean.
2. Enter height in centimetres under Metric, or in inches under Imperial. A height of 1.75 metres is 175 centimetres; five feet nine inches is 69 inches.
3. Enter weight in kilograms under Metric, or pounds under Imperial. One pound is 0.453592 kilograms, so 160 pounds is 72.6 kilograms.
4. Optionally fill in age and gender. They are recorded on the form for context; the standard adult BMI formula and its bands do not vary with either, so they do not change the result.
5. Read the output. The figure is followed by the band and the risk line, and the normal-weight range for your height is given in whichever unit you selected.

Reading the Six Bands

The bands are fixed thresholds and the page applies them in order, testing the lowest first. Every boundary belongs to the upper band, so a BMI of exactly 25.0 is Overweight rather than the top of Normal weight.

• Below 18.5 is Underweight. The page's note points at possible undernutrition rather than treating a low figure as automatically good, which is the correct reading — a BMI of 17 is not a healthier version of 22.
• 18.5 up to but not including 25 is Normal weight, described as low health risk.
• 25 up to 30 is Overweight, with a note about increased risk of heart disease and diabetes.
• 30 up to 35 is Obese Class I, 35 up to 40 is Class II, and 40 and above is Class III, each with a progressively stronger risk description. The three obesity classes exist because risk rises continuously rather than jumping at a single line.
• The same result also states the weight range that would place you in the normal band at your height, computed from 18.5 and 24.9 multiplied by your height in metres squared and converted back to pounds if you selected Imperial.

Where the Index Stops Being Useful

These are the cases where a BMI figure should be set aside rather than interpreted, and they are not edge cases — they cover a large share of the population.

• Athletes and anyone carrying significant muscle mass. A rugby forward and a sedentary person of the same height and weight receive identical figures, and only one of them has a weight-related health risk.
• Children and teenagers. Growth charts and age-and-sex-specific percentile curves are used instead, because the healthy range shifts rapidly through adolescence. Adult bands applied to a fourteen-year-old produce meaningless results.
• Pregnancy, where the weight being measured is not the person's own and the index simply does not apply.
• Older adults, where the relationship between BMI and mortality flattens and shifts upward; a figure that looks borderline in mid-life carries a different meaning at eighty.
• People of different body builds at the same height. The thresholds were derived largely from European-ancestry populations, and several health bodies now apply lower overweight cut-offs for people of South Asian descent because cardiometabolic risk rises at a lower BMI.
• Anyone whose weight has changed quickly. The index cannot distinguish fat gained from fluid retained, and the two call for entirely different responses.

What to Measure Alongside It

Alternative	Notes
Waist circumference	Measures where fat is stored, which matters more for metabolic risk than the total. The conventional thresholds are 94 cm for men and 80 cm for women, with lower figures recommended for South Asian populations. A normal BMI with a large waist is a real combination.
Waist-to-height ratio	Waist divided by height, with 0.5 widely used as a simple threshold. Uses the same kind of arithmetic as BMI but tracks central fat, which is the component most associated with cardiovascular risk.
Waist-to-hip ratio	Adds distribution to the picture. A WHtR or WHR in the risky range alongside an unremarkable BMI is the pattern most worth discussing with a clinician.
Body fat percentage	The measurement BMI is often mistaken for. Requires equipment — callipers, a scale using bioelectrical impedance, or a DEXA scan — none of which are available from a browser.
Trend over time	The most useful measurement available with no equipment at all. One reading is a snapshot; a change over six months, measured the same way, tells you what a single figure cannot.

BMI Questions

Is BMI accurate for an individual?

It is a screening measure and it is best read as one. For a whole population the relationship between BMI, body fat and health outcomes is strong enough to be useful. For one person at one moment it can be misleading in both directions: a muscular athlete can land in the overweight band with low body fat, and someone with little muscle can land in the normal band with a high fat proportion. Waist measurements close part of that gap.

Why does the tool ask for age and gender if they do not change the result?

They are collected because people expect to supply them and because they belong on a health form. The adult BMI formula is deliberately independent of both — that independence is exactly why the index works as a screening tool, since it needs nothing beyond a height and a weight. Different bands apply to children, and those bands require a percentile chart rather than a formula.

What is a healthy BMI?

The conventional normal band is 18.5 to 24.9. It is worth treating it as a band rather than a target, and worth noting that it is not the same as an ideal. A figure at the lower end is not automatically better than one in the middle — the health outcomes associated with the band are broadly similar across it, and the risks of being underweight are real.

Can I use this for my child?

No. Children and adolescents need age-and-sex-specific percentile curves, because both the healthy range and the meaning of a given figure change as a child grows. A number that would be unremarkable in an adult can be a concern in a nine-year-old, and the reverse. Ask a paediatrician for the appropriate chart.

Is my height and weight sent anywhere?

No. The calculation is a few lines of JavaScript running in the page, and the form has no network call attached to it. Nothing is stored, and closing the tab leaves no record on the device.

Last verified: October 7, 2026

Launch BMI Calculator

All Tools · All Tools · About · How We Test · Contact · Privacy

Maintained by Huang Bin · Last updated October 3, 2026