BMI Calculator
Enter your height and weight to see your body mass index, where it sits on the WHO scale and the normal weight range for your height.
- WHO categories
- Metric and US units
- Live result
- Nothing stored
How to calculate your BMI
Two measurements are all it takes.
- 1
Choose your units
Metric (centimetres and kilograms) or US units (feet, inches and pounds).
- 2
Enter height and weight
Measure without shoes and weigh yourself in light clothing for a consistent result.
- 3
Read the result
You get your BMI, its category, the normal weight range for your height and your position on the scale.
More than a single number
Context that makes the BMI easier to interpret.
WHO categories
From underweight to obesity class III, using the World Health Organization thresholds for adults.
Healthy weight range
The weights that correspond to a BMI of 18.5 to 25 at your height, in kg or lb.
Visual scale
A coloured scale shows at a glance where your value sits.
Both unit systems
Switch between metric and US units; the example values adapt.
BMI Prime and ponderal index
Two extra measures: your BMI relative to the upper normal limit, and an index that scales better for very tall or short people.
Copy the result
One tap copies the full result as tidy text for a message, a note or a spreadsheet.
Made for phones
Large fields, the right keyboard for numbers and a layout that fits small screens.
Nothing is stored
Your body data is calculated in your browser and is never saved or sent anywhere.
What the body mass index tells you — and what it does not
The body mass index relates weight to height: BMI = weight in kg ÷ (height in m)². Someone who is 1.75 m tall and weighs 70 kg has a BMI of 70 ÷ 3.0625 = 22.9. With US units the formula is 703 × weight in lb ÷ (height in inches)².
For adults aged 20 and over, the World Health Organization classifies a BMI below 18.5 as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight and 30 or more as obesity. These ranges describe statistical health risk across populations; they are a screening tool, not a diagnosis.
The BMI cannot tell muscle from fat, so athletic people can land in the “overweight” range with a low body-fat percentage, while older adults with little muscle can have a “normal” BMI and still carry too much fat. Waist circumference adds useful information. For children and teenagers, BMI is assessed with age- and sex-specific percentile charts instead of these fixed ranges.
WHO BMI categories for adults
| BMI | Category | Note |
|---|---|---|
| Below 18.5 | Underweight | Below 16 is classed as severe thinness |
| 18.5 – 24.9 | Normal weight | Lowest statistical health risk |
| 25.0 – 29.9 | Overweight (pre-obesity) | Risk rises with waist circumference |
| 30.0 – 34.9 | Obesity class I | Medical advice recommended |
| 35.0 – 39.9 | Obesity class II | |
| 40.0 and above | Obesity class III |
Tips
- Curious how many calories your body uses per day? Continue with the Calorie Calculator.
- Tracking a weight change in percent? The Percentage Change Calculator does it in one step.
- Need your exact age for a form or a check-up? Use the Age Calculator.
- Measure at the same time of day, ideally in the morning: body weight varies by 1–2 kg over the day.
Frequently asked questions
Can’t find your answer? Contact us — we reply quickly.
What is a healthy BMI?
For adults the WHO defines 18.5 to 24.9 as the normal range. For people of Asian descent, some health authorities use lower action points of 23 and 27.5 because health risks appear at lower values.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703 and divide by your height in inches squared. Example: 154 lb and 69 in → 703 × 154 ÷ 4,761 = 22.7.
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so muscular people can have a high BMI without excess body fat. Body-fat measurements or waist circumference are more informative in that case.
Does the same scale apply to men and women?
Yes, the adult WHO ranges are the same for both sexes, although women typically have a higher body-fat percentage at the same BMI.
Can I use this calculator for children?
No. For under-20s, BMI must be compared with age- and sex-specific growth charts. Ask a paediatrician or use a dedicated child BMI percentile tool.
Is my data stored?
No. Height, weight and age are processed in your browser only. They are not saved on your device and are never sent to a server.
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