BMI Calculator - Body Mass Index in Metric & Imperial
Get your body mass index, WHO weight category and the healthy weight range for your height — in metric or imperial units, with a visual BMI scale.
BMI 25.4 — Overweight
A BMI at or above 25 is associated with a higher risk of type 2 diabetes, high blood pressure and heart disease.
WHO BMI categories for adults
| Category | BMI range | Weight at your height |
|---|---|---|
| Underweight | 0 – 18.5 | 0.0 kg – 54.7 kg |
| Healthy weight | 18.5 – 25 | 54.7 kg – 74.0 kg |
| Overweight | 25 – 30 | 74.0 kg – 88.8 kg |
| Obesity class I | 30 – 35 | 88.8 kg – 103.5 kg |
| Obesity class II | 35 – 40 | 103.5 kg – 118.3 kg |
| Obesity class III | 40 and above | above 118.3 kg |
BMI is a screening measure, not a diagnosis. It does not distinguish muscle from fat, so athletes often read as "overweight", and it is not valid for children, pregnant women or the very elderly. Talk to a healthcare professional about your individual health.
What is BMI?
Body mass index puts weight in the context of height. It is your weight in kilograms divided by your height in metres squared, giving a single number that can be compared against population thresholds. It was designed as a population-level screening measure, and that is exactly how it should be read: a quick flag worth investigating, not a diagnosis.
Metric: BMI = kg ÷ m²
Imperial: BMI = 703 × lb ÷ in²
WHO BMI Categories for Adults
- Below 18.5 — underweight
- 18.5 to 24.9 — healthy weight
- 25.0 to 29.9 — overweight
- 30.0 to 34.9 — obesity class I
- 35.0 to 39.9 — obesity class II
- 40.0 and above — obesity class III
The calculator also shows the actual weight range that corresponds to each category at your height, which is usually more useful than the BMI number itself.
What the Calculator Gives You
Your BMI
Calculated to two decimals with your WHO category.
Healthy Range
The actual weight range for a BMI of 18.5 to 24.9 at your height.
Distance to Range
How much to gain or lose to reach the healthy band.
Visual Scale
See where you sit on the 15 to 40 BMI band.
BMI Prime
Your BMI as a ratio of the upper healthy limit of 25.
Both Unit Systems
Metric centimetres and kilograms, or feet, inches and pounds.
How to Calculate Your BMI
- Choose metric or imperial units.
- Enter your height.
- Enter your weight.
- Read your BMI, category and healthy weight range instantly.
Where BMI Falls Short
BMI has one input beyond height: total weight. It cannot tell what that weight is made of, and that is its central limitation:
- Muscle reads as fat. Muscle is denser than fat, so athletes and regular weight trainers frequently score as overweight despite very low body fat.
- Fat distribution is invisible. Visceral fat around the abdomen carries far more metabolic risk than fat on the hips and thighs, but BMI treats them identically. Waist circumference and waist-to-height ratio capture this better.
- Older adults lose muscle. Someone can lose lean mass and gain fat while their BMI stays unchanged.
- Children need percentiles. Adult cut-offs do not apply — children and teenagers are assessed against age- and sex-specific growth charts.
- Ethnicity matters. Several health bodies use lower thresholds for people of South Asian, Chinese and other Asian descent, where cardiometabolic risk rises at a lower BMI.
What BMI Is Still Good For
Despite the caveats, BMI remains useful because it is cheap, reproducible and correlates well with health outcomes across large groups. For most people who are not highly muscular, it gives a reasonable first indication of whether weight is worth discussing with a doctor. Used alongside waist measurement, blood pressure and blood markers, it is a sensible starting point rather than a verdict.
Who This Calculator Is For
- Adults checking whether their weight is in the healthy range
- Anyone setting a target weight before starting a plan
- People tracking progress over time
- Health and fitness professionals doing quick screening
- Anyone completing a health or insurance questionnaire
❓ Frequently Asked Questions
What is BMI?
Body mass index is your weight in kilograms divided by your height in metres squared. It is a quick screening measure that puts weight in the context of height.
What is a healthy BMI?
The WHO classifies 18.5 to 24.9 as a healthy weight for adults, below 18.5 as underweight, 25 to 29.9 as overweight, and 30 or above as obese.
How do I calculate BMI in imperial units?
BMI = 703 × weight in pounds ÷ (height in inches)². The calculator does this for you when you switch to imperial.
What is my healthy weight range?
It is the weight that puts your BMI between 18.5 and 24.9 at your height. The calculator shows that range in your chosen units, along with how far you are from it.
Is BMI accurate for athletes?
No. BMI cannot tell muscle from fat, so muscular people often register as overweight despite low body fat. Body fat percentage or waist measurement is more informative for them.
Does BMI work for children?
Not in this form. Children and teenagers are assessed against age- and sex-specific percentile charts rather than fixed adult cut-offs.
What is BMI prime?
BMI prime is your BMI divided by 25, the upper limit of the healthy range. A value below 1.0 means you are within the healthy range; 1.2 means you are 20% above the upper limit.
Should BMI thresholds differ by ethnicity?
Some health bodies use lower cut-offs for people of South Asian, Chinese and other Asian descent because cardiometabolic risk rises at a lower BMI. Ask your doctor which thresholds apply to you.
What are the health risks of a high BMI?
A BMI at or above 25 is associated with a higher risk of type 2 diabetes, high blood pressure, heart disease, sleep apnoea and some cancers — though individual risk depends on many other factors.
Is this medical advice?
No. BMI is a screening tool, not a diagnosis. Discuss your results with a healthcare professional who can assess your full health picture.