Visual WHO scale
An animated gauge places your result across every category from underweight to obesity class III, so you can see how close you are to the next band instead of guessing.
Free · Metric & imperial · Private
BMI Calculator — Body Mass Index & Healthy Weight Range
Work out your body mass index in seconds, see exactly where it sits on the WHO scale, and get the healthy weight range for your height — plus the waist-to-height ratio that BMI alone can’t tell you.
kg/cm and ft/in/lb
Healthy weight range
Waist-to-height ratio
No sign-up, nothing stored
Calculate your BMI
Enter your height and weight. Everything is calculated in your browser — no data is uploaded or saved.
Your BMI result will appear here
Add your height and weight and you’ll get your BMI, its category on the WHO scale, your healthy weight range and a full breakdown.
Why this calculator
A BMI calculator that gives you context, not just a number
A bare BMI figure tells you very little on its own. This tool shows where you sit on the scale, what the healthy range means in real kilograms or pounds, and where BMI is known to be unreliable.
Your healthy weight range
We convert the 18.5–24.9 band into an actual weight range for your height, in your chosen units, so the target is concrete rather than abstract.
Waist-to-height ratio
Add a waist measurement and you also get WHtR, a widely used indicator of central fat that BMI misses entirely. Few calculators offer both together.
Honest about the limits
BMI does not distinguish muscle from fat and reads differently across ages and ethnic groups. We say so clearly rather than presenting one number as a verdict.
Metric and imperial, instantly
Switch between cm/kg and ft/in/lb without retyping or hunting for a converter. Feet and inches are handled as separate fields, the way people actually think.
Private and ad-light
No account, no email capture and no health data leaving your device. It loads fast and works comfortably one-handed on a phone.
How to use it
How to calculate your BMI in four steps
Pick your units
Choose metric or imperial. The fields change to match, so you never have to convert anything by hand.
Enter height and weight
Measure without shoes and ideally in the morning. Small daily fluctuations are normal and expected.
Add waist and age
Both are optional. Waist unlocks the waist-to-height ratio; age flags whether adult categories apply.
Read the full result
You get your BMI, its category, your healthy weight range and how far you are from each boundary.
Benefits
What your BMI is useful for — and what it isn’t
BMI is a screening tool. It is quick, free and reasonably good at flagging when a conversation with a clinician is worth having, but it was never designed to describe an individual body.
A quick population-level screen
It is the measure most health services use first, so knowing yours helps you understand the numbers on your records.
A concrete healthy range
Seeing the range in kilograms or pounds for your height is far more useful than an abstract index value.
Context for a doctor’s visit
Bringing your BMI and waist ratio to an appointment makes the discussion more specific and less guesswork.
Trend tracking over time
The direction of travel over months is more informative than any single reading on any single day.
Not a measure of health or worth
It says nothing about fitness, diet quality, blood pressure, bloods or how you feel day to day.
Not a body composition test
Muscle weighs more than fat, so athletes often read as overweight while carrying very little body fat.
The method
How BMI is calculated
The BMI formula
In metric units, BMI is your weight in kilograms divided by the square of your height in metres: BMI = kg ÷ m². Someone who is 1.70 m and 68 kg has a BMI of 68 ÷ 2.89, which is 23.5.
In imperial units the formula is BMI = (lb ÷ in²) × 703. The 703 factor simply converts pounds and inches into the metric result, so both formulas give the same answer.
The standard BMI categories
| Category | BMI range | Notes |
|---|---|---|
| Underweight | Below 18.5 | Worth discussing with a clinician |
| Healthy weight | 18.5 – 24.9 | The reference range for most adults |
| Overweight | 25.0 – 29.9 | Called pre-obesity by the WHO |
| Obesity class I | 30.0 – 34.9 | Moderate |
| Obesity class II | 35.0 – 39.9 | Severe |
| Obesity class III | 40.0 and above | Very severe |
Where BMI is least reliable
- Muscular or athletic builds, where high lean mass pushes BMI up without excess body fat.
- Older adults, who tend to lose muscle and may carry more fat at the same BMI.
- People of South Asian, Chinese and some other ancestries, for whom lower thresholds — often 23 for overweight and 27.5 for obesity — are recommended.
- Children and teenagers under 20, who are assessed on age and sex percentiles, not adult categories.
- Pregnancy, where BMI is not a meaningful measure at all.
Why waist-to-height ratio is a useful companion
Two people can share a BMI while carrying weight very differently. Waist-to-height ratio — your waist measurement divided by your height in the same units — captures central fat, which is more closely tied to metabolic risk. A common rule of thumb is to keep your waist under half your height, so a ratio below 0.5. Because both measurements use the same units, the ratio works identically in centimetres or inches.
FAQ
BMI calculator questions, answered
How do I calculate my BMI manually?
In metric, divide your weight in kilograms by your height in metres squared. For example, 68 kg at 1.70 m is 68 ÷ (1.70 × 1.70) = 23.5. In imperial, divide your weight in pounds by your height in inches squared and multiply by 703. Both routes produce the same figure.
What is a healthy BMI range for adults?
The World Health Organization defines 18.5 to 24.9 as the healthy range for adults. Below 18.5 is classed as underweight, 25 to 29.9 as overweight and 30 or above as obesity. Some health bodies recommend lower thresholds for people of South Asian and East Asian descent, typically 23 and 27.5.
Is BMI different for men and women?
The formula and the adult category thresholds are identical for both. Women generally carry a higher proportion of body fat than men at the same BMI, which is one reason BMI is treated as a rough screening measure rather than a body composition test.
Is BMI accurate for athletes and muscular people?
Often not. BMI uses only height and weight, so it cannot tell muscle from fat. A well-trained athlete can register as overweight or even obese while carrying very little body fat. In those cases waist measurement, body fat percentage or a clinical assessment gives a far more meaningful picture.
Can I use this BMI calculator for children?
Not for a diagnosis. From age 2 to 19, BMI is interpreted against age and sex growth percentiles rather than fixed adult categories, so the same number means different things at different ages. The calculator will still show the value, but a paediatrician or child health chart should be used to interpret it.
What is a good waist-to-height ratio?
A widely used guide is to keep your waist below half your height, which means a ratio under 0.5. Between 0.5 and 0.6 is generally treated as increased risk and above 0.6 as high. Measure at the level of your navel, at the end of a normal breath out, without pulling the tape tight.
How often should I check my BMI?
Every few months is plenty. Weight fluctuates by one to two kilograms across a normal day and week because of hydration, food and hormones, so frequent checks tend to show noise rather than change. If you have concerns about your weight in either direction, a clinician can interpret it alongside blood pressure, blood tests and your medical history.
Check your BMI and healthy weight range now
Free, private and instant — with the WHO scale, your healthy weight range in real units and the waist-to-height ratio most calculators leave out.
This BMI calculator is provided for general information and screening purposes only. It is not medical advice, it cannot diagnose any condition, and it does not measure body composition or overall health. Always speak with a doctor or another qualified healthcare professional about your weight, your results and any decisions about your care.