BMI Calculator
Your body mass index, your category, and the healthy weight range for your height.
What is the BMI Calculator?
The BMI Calculator works out your body mass index from your height and weight, tells you which WHO category it falls into, and shows the healthy weight range for your exact height. Enter metric (kg, cm) or imperial (lb, ft/in) units — both use the same underlying formula, just scaled differently. BMI is the screening measure doctors, insurers and fitness apps use because it needs only two numbers and no special equipment, not because it is a precise measure of body fat. This calculator gives you the number quickly and explains what it does and does not tell you.
A single BMI number hides a lot. Two people with the same height and the same BMI can have very different amounts of muscle versus fat, and the standard adult categories were built from population data that does not describe children, pregnant women or highly muscled athletes well. Use the result as a starting point for a conversation with a professional, not as a diagnosis.
Why use a free bmi calculator?
Metric and imperial, same calculation
Switch between kg/cm and lb/ft-in without converting anything by hand. Both paths use the same formula scaled to the unit system.
Category and healthy range together
You get more than the number — the WHO category it falls in, and the weight range that would put you in the "normal" band at your current height.
The formula is shown, not hidden
See exactly how your BMI was calculated, so you can check it or explain it to someone else.
Honest about the limits
BMI cannot separate muscle from fat and is not the right tool for children, pregnant women or elite athletes. This page says so directly instead of pretending otherwise.
Nothing is uploaded
Your height and weight are processed in your browser and never sent to a server.
How do you use the BMI Calculator?
- 1
Choose metric or imperial
Metric uses kilograms and centimetres. Imperial uses pounds and feet/inches. Pick whichever matches how your height and weight are usually recorded.
- 2
Enter your height and weight
Type the two numbers. There is no need to convert units yourself first.
- 3
Read your BMI and category
The result shows your BMI to one decimal place and the WHO category it falls into — underweight, normal, overweight or one of the obesity classes.
- 4
Check the healthy weight range
The calculator also shows the weight range that corresponds to a "normal" BMI at your specific height, so you can see how far you are from it in kilograms or pounds rather than just in BMI points.
How is bmi calculator calculated?
BMI = weight (kg) ÷ height (m)²Where:
- weight (kg)
- Body weight in kilograms
- height (m)
- Height in metres — divide centimetres by 100
- Imperial version
- BMI = 703 × weight (lb) ÷ height (in)² — the 703 constant converts pounds and inches into the same scale as the metric formula
The simple version
Divide your weight by your height squared. In metric, weight is in kilograms and height in metres, so a 70 kg person who is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In imperial, the numbers are in pounds and inches, so a 703 multiplier is added to bring the result onto the same 15–40 scale.
What does it look like in practice?
Metric calculation
Input
70 kg, 175 cm (1.75 m)
Result
BMI 22.9 — Normal weight
70 ÷ (1.75²) = 70 ÷ 3.0625 = 22.86, rounded to 22.9. This falls inside the 18.5–24.9 "normal weight" band.
Imperial calculation
Input
160 lb, 5 ft 6 in (66 in)
Result
BMI 25.8 — Overweight
703 × 160 ÷ (66²) = 112,480 ÷ 4,356 = 25.82. That crosses the 25.0 threshold into the "overweight" category by a small margin.
Same BMI, different healthy-range framing
Input
90 kg, 180 cm (1.80 m)
Result
BMI 27.8 — Overweight. Healthy range for 180 cm: 59.9–80.9 kg
The calculator also expresses the target range as a weight, which is easier to act on than "get your BMI 3 points lower".
How accurate is it?
BMI is calculated exactly from the formula above — there is no estimation in the arithmetic. The uncertainty is not in the maths, it is in what BMI actually measures: it uses total body weight and cannot distinguish muscle, fat, bone or water, so the category it reports is a population-level screening signal, not an individual diagnosis.
- A muscular person can show as "overweight" or "obese" by BMI while having low body fat — this is the most common false positive. The Body Fat Calculator estimates composition directly instead of inferring it from weight and height.
- The standard adult categories (underweight, normal, overweight, obese) do not apply to children and teenagers, who need age- and sex-specific percentile charts instead.
- The World Health Organization publishes separate, lower cut-offs for adults of Asian descent (overweight from 23, obese from 27.5) because health risk rises at a lower BMI in Asian populations. This calculator uses the standard global cut-offs; check which set applies if you are being screened clinically.
- BMI is not designed for use during pregnancy, and standard categories do not apply.
- This is a screening calculation, not medical advice. A result outside the "normal" band is a prompt to talk to a healthcare professional, not a diagnosis on its own.
What should you know before using it?
The WHO adult BMI categories used by this calculator:
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese (Class I) |
| 35.0 – 39.9 | Obese (Class II) |
| 40.0 and above | Obese (Class III) |
Which tools relate to the bmi calculator?
The bmi calculator is one of 21 calculators on this site. These are the ones most often used alongside it — either because they handle the next step in the same job, or because they answer a question this tool raises.
Body Fat Calculator
Estimates the percentage of your weight that is fat, which is what BMI is actually trying to proxy for. Use it when BMI looks off for your build.
Age Calculator
BMI interpretation depends on age — the adult categories on this page do not apply to a child's or teenager's BMI, which is read against age-and-sex percentiles instead.
Calorie Calculator
If your goal is to move your weight toward the healthy range this page shows, the calorie calculator gives you the daily intake target to get there.
Heart Rate Calculator
Training heart-rate zones are derived from age, not weight — useful alongside BMI when the goal is fitness rather than a number on a chart.
When should you use a bmi calculator?
Because the bmi calculator runs entirely in your browser, it suits work you would not want to hand to a third-party server — client files, unpublished drafts, anything under an NDA. These are the situations people reach for it in most often.
Personal health tracking
A quick check-in figure to track alongside other measures, not a replacement for a clinical assessment.
Medical and insurance screening
Many intake forms and insurance questionnaires ask for BMI directly because it is cheap to compute from height and weight alone.
Fitness and nutrition planning
A starting reference point when setting a weight or body-composition goal, best used together with the Body Fat and Calorie calculators.
Open the Fitness and nutrition planningSports eligibility bands
Some weight-class and youth sports categories reference BMI or the underlying weight range alongside other criteria.
Frequently asked questions
What is a healthy BMI?
Is BMI accurate for athletes?
How is BMI calculated?
Is BMI different for men and women?
Does a BMI chart apply to children?
Why do some countries use different BMI cut-offs?
What is the healthy weight range for my height?
Is the bmi calculator safe to use?
This tool runs entirely inside your browser. Your text, files and settings are processed on your own device and are never uploaded to our servers — there is nothing for us to store, log or leak. You can confirm it yourself: open your browser DevTools, switch to the Network tab, and use the tool. You will not see an upload request. It also means the tool keeps working if your connection drops mid-task.
Where do these figures come from?
Every method, threshold and standard this page relies on, with a link to the document that defines it. Check them — a tool that will not show its sources is asking you to take its word for it.
- 1Body mass index — BMI
World Health Organization, Regional Office for Europe · 2010
Supports: The 18.5–24.9 normal-weight band and the underweight, overweight and obese Class I/II/III thresholds used in the category table.
- 2Obesity and overweight
World Health Organization · 2024
Supports: The general BMI ≥25 (overweight) and BMI ≥30 (obese) definitions used across the page.
- 3Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies
WHO Expert Consultation, The Lancet · 2004
Supports: The lower BMI cut-offs (overweight from 23, obese from 27.5) cited for adults of Asian descent.
Read more about bmi calculator
What is BMI and How Should You Interpret Your Body Mass Index?
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