BMI Calculator
Check your Body Mass Index from height and weight, with your healthy range.
Formula
Body Mass Index = weight (kg) ÷ height (m)². WHO categories: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese.
Worked example
A person 175 cm tall weighing 70 kg: height in meters = 1.75, BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9 — normal weight.
How to use the BMI calculator
- Enter your height in centimeters (for example, 175).
- Enter your weight in kilograms (for example, 70).
- Read your result: your BMI to one decimal place, your WHO weight category, and the healthy weight range for your height.
This calculator uses metric units only. If you know your height and weight in feet, inches or pounds, convert them first (see the imperial section below).
Worked example: 175 cm, 70 kg
- Convert height to meters: 175 ÷ 100 = 1.75 m
- Square the height: 1.75 × 1.75 = 3.0625
- Divide weight by that number: 70 ÷ 3.0625 = 22.857…
- BMI = 22.9, which falls in the Normal category.
For a height of 175 cm, a BMI between 18.5 and 24.9 corresponds to roughly 56.7 kg to 76.3 kg.
BMI categories and what they mean
The World Health Organization groups adult BMI into four categories. These are screening ranges, not a diagnosis. For the WHO's own guidance, see their fact sheet on overweight and obesity.
- Underweight (below 18.5): Consider checking in with a doctor or dietitian, especially if you've lost weight without trying or feel tired often.
- Normal (18.5 to 24.9): Keep up regular movement and balanced meals, and use this number as one check among several rather than a target to chase.
- Overweight (25 to 29.9): Small, steady changes such as more daily walking or swapping sugary drinks for water are a sensible place to start.
- Obese (30 and above): Book a conversation with your doctor, who can look at the full picture and suggest options that suit you.
Your result is a starting point for a conversation, not a verdict. A doctor can tell you what your number means for you personally.
What BMI doesn't tell you
BMI only uses height and weight. It has no way of knowing what that weight is made of.
Muscle and fat look the same
Muscle is denser than fat. An athlete or regular weightlifter can have a BMI in the "overweight" range while carrying very little body fat. The reverse happens too: someone with low muscle mass can land in the "normal" range while carrying more fat than the number suggests.
Pregnancy and older adults
BMI isn't designed for use during pregnancy, so weight gain is tracked differently by your midwife or doctor. In older adults, muscle loss can shift body composition without changing weight much, so the standard categories can be less informative.
Children and teens
The adult cutoffs above don't apply under 18. Young people's BMI is compared with percentiles for their age and sex, because growth changes what's typical. If you're unsure whether adult categories apply, you can check your exact age first.
Waist circumference is a useful companion
Where you carry weight matters. Extra weight around the waist is linked with higher health risk, so measuring your waist alongside BMI gives a fuller picture. Your doctor or nurse can show you how to measure it properly. The CDC's guide to BMI explains how these measures fit together.
The BMI formula (metric and imperial)
Metric formula
BMI = weight (kg) ÷ height (m)²
Example: 70 kg and 1.75 m. Height squared is 3.0625, and 70 ÷ 3.0625 = 22.9.
Imperial formula
BMI = 703 × weight (lb) ÷ height (in)²
Example: 154 lb and 69 inches. Height squared is 4,761. Then 703 × 154 = 108,262, and 108,262 ÷ 4,761 = 22.7.
The two examples are close but not identical because 154 lb and 69 in are rounded equivalents of 70 kg and 175 cm. To use this calculator with imperial measurements, multiply inches by 2.54 to get centimeters, and multiply pounds by 0.4536 to get kilograms.
Frequently asked questions
What is a healthy BMI?
For adults, the WHO “normal” range is 18.5 to 24.9. A BMI in this range is generally associated with lower health risk at a population level, but it doesn't guarantee good health for any one person.
Is BMI accurate?
BMI is a quick screening tool, not a measure of health or body fat. It works reasonably well across large groups but can mislead for individuals, especially athletes, older adults and people with unusual body composition.
How is BMI calculated?
Divide your weight in kilograms by your height in meters squared. For example, 70 kg at 1.75 m gives 70 ÷ 3.0625 = 22.9.
Does muscle affect BMI?
Yes. BMI can't distinguish muscle from fat, so a muscular person may get a higher BMI than their body fat would suggest. That's why a result in the “overweight” range isn't automatically a concern for someone who trains regularly.
What should I do if my BMI is in the obese range?
Talk to your doctor. They can consider your waist measurement, blood pressure, family history and other factors, then suggest next steps that fit your situation. A BMI result alone isn't a diagnosis.
