BMI Calculator
Calculate your Body Mass Index (BMI) instantly. This free BMI calculator takes your height and weight, shows your category, and reveals the healthy weight range for your height - in metric or imperial units.
BMI is the most widely used screening tool for healthy weight: a single number that relates your weight to your height so you can quickly see whether you fall in the underweight, healthy, overweight, or obese band. It is the metric doctors, insurers, and researchers reach for first because it is fast, free, and consistent across populations - and it is a useful starting point for setting a realistic weight-loss or muscle-gain goal.
On this page you will learn what your BMI number means, the exact formula behind it, the healthy weight range for your height, and where BMI falls short (and what to use instead). Enter your height and weight above to get your result, then read on to put it into context.
Your Body Mass Index
Normal
18.5-24.9 - a healthy range for most adults.
Healthy weight range
For your height (BMI 18.5-24.9)
50–68 kg
How it works
1
Enter height and weight
Use metric (cm/kg) or imperial (ft/lb) - the calculator converts automatically.
2
See your BMI
We compute kg/m² and place you on the underweight-to-obese scale.
3
Get your healthy range
We show the weight range that keeps you in the healthy BMI band for your height.
How BMI is calculated
Body Mass Index is a height-adjusted weight measure. The formula divides your weight in kilograms by the square of your height in meters, giving a value in units of kg/m². Squaring the height accounts for the fact that taller people naturally carry more weight for the same body shape, so the index stays comparable across statures.
Metric formula
BMI = weight (kg) ÷ height (m)²
Imperial formula
BMI = 703 × weight (lb) ÷ height (in)²
Worked example: a person who is 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9, which sits comfortably in the healthy range. In imperial units the same person (154 lb, 69 in) gives 703 × 154 ÷ (69 × 69) ≈ 22.9. This calculator runs both conversions behind the scenes, so you can type whichever units you know and still get an accurate result.
Understanding your result
Your BMI lands in one of five adult categories. Here is what each band means and the typical next step for each:
| BMI range | Category | What it suggests |
|---|---|---|
| Below 18.5 | Underweight | May lack nutrients; consider adding calorie-dense foods. |
| 18.5 - 24.9 | Healthy weight | Lowest risk for weight-related disease; maintain habits. |
| 25.0 - 29.9 | Overweight | Aim for a modest calorie deficit to trend down. |
| 30.0 - 34.9 | Obese (class I) | Lifestyle changes advised; talk to your doctor. |
| 35.0 and above | Obese (class II-III) | Higher risk; seek structured medical support. |
BMI is a screening signal, not a diagnosis. It does not measure body fat directly, so a very muscular person can read high without being over-fat, and an older adult can read "healthy" while having low muscle mass. Pair your BMI with a waist measurement (under 94 cm/37 in for men, 80 cm/31.5 in for women is lower risk) and use the calculator above to see the weight range that would keep you in the healthy band for your height.
Frequently Asked Questions
What is a healthy BMI?
A healthy BMI for most adults is between 18.5 and 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is obese. This calculator shows your exact category and a healthy weight range for your height.
How is BMI calculated?
BMI = weight in kilograms divided by height in meters squared (kg/m²). In imperial units it is 703 x weight in pounds divided by height in inches squared. This calculator handles the conversion for you in either unit system.
Is BMI accurate for athletes?
BMI does not distinguish between muscle and fat, so very muscular athletes can register as overweight or obese despite low body fat. For a body-composition check that accounts for muscle, try our body fat calculator using the Navy method.
What BMI is considered overweight?
A BMI of 25 to 29.9 is classified as overweight, and 30 or above as obese, for adults aged 20 and over. These cut-offs come from the WHO and are based on the link between BMI and chronic-disease risk. A single BMI number is a screening signal, not a diagnosis - your doctor will weigh it against waist size, blood work, and lifestyle.
Does BMI work for older adults and children?
For adults 65 and over, a slightly higher BMI (around 23-30) is often associated with better survival, so the standard bands are less strict. BMI is not used as-is for children; pediatricians plot BMI on age- and sex-specific percentile charts instead. Pregnant and breastfeeding people should also not rely on standard BMI bands.
What is a healthy weight range for my height?
Your healthy weight range is the weight that lands your BMI between 18.5 and 24.9 for your exact height. This calculator works it out automatically once you enter your height - just look for the healthy range shown beneath your result, in metric or imperial units.
How often should I check my BMI?
Checking monthly is plenty for most people, because day-to-day weight shifts by 1-2 kg from water, food, and hormones. Track the trend over weeks rather than reacting to a single reading, and pair BMI with waist circumference for a fuller picture of healthy weight.
Is this BMI calculator free?
Yes - completely free with no sign-up. Your height and weight are saved in your browser and encoded in the URL so you can bookmark or share your result. Nothing is sent to a server.
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