BMI Calculator
Calculate your Body Mass Index (BMI) to determine if your weight is in a healthy range for your height. Get instant results with our free online BMI calculator that supports both metric and imperial units.
How to Use
- 1
Select your unit system: Metric (kg, cm) or Imperial (lbs, inches)
- 2
Enter your biological sex and whether you have an athletic body type
- 3
Input your weight
- 4
Input your height
- 5
Check "Athletic body type" if you have above-average muscle mass — this adjusts the interpretation
- 6
View your BMI score, category, health risk, healthy weight range, and BMI Prime
- 7
Understanding the key inputs — BMI Prime is your BMI divided by 25 (the upper normal range), so a value under 1.0 means you are in the normal range
- 8
Interpreting the results — the healthy weight range shows what weight range is considered normal for your height
Examples
Good Examples
Average adult (metric)
70 kg ÷ (1.70 m)² = 24.2 (Normal weight)Average adult (imperial)
154 lbs ÷ (71 in)² × 703 = 21.5 (Normal weight)Checking if weight loss is needed
A 5'6" person weighing 180 lbs has BMI 29.0 — losing 15 lbs brings them to 26.5 (overweight to normal)Understanding BMI Prime
A BMI of 22.5 gives BMI Prime of 0.90 — well within the healthy range (target: 0.74 to 1.0)Healthy weight range for planning
A 175 cm person's healthy range is 57–77 kg — this helps set realistic weight loss or gain goalsBad Examples
Using BMI for athletes
A bodybuilder with 80 kg muscle at 170 cm has BMI 27.7 "overweight" despite low body fatMixing metric and imperial
Entering weight in kg but height in inches gives a meaningless resultComparing BMI across different ethnicities without adjustment
Some health organizations recommend lower BMI thresholds for Asian populations due to different body composition patternsCommon Mistakes
- Using BMI as the sole health indicator — it doesn't distinguish between muscle and fat mass
- Mixing unit systems — use either metric (kg, cm) or imperial (lbs, inches), not a mix
- Applying adult BMI to children — children need age-specific BMI percentile charts
- Ignoring body frame size — people with larger frames naturally weigh more
- Forgetting that BMI doesn't account for fat distribution — where fat is stored matters for health
- Assuming BMI changes are linear with weight — BMI uses height squared, so small height differences matter more than expected
- Not distinguishing between overweight and obese categories — BMI 25-30 and 30+ carry very different health risks
- Confusing BMI Prime with BMI — BMI Prime normalizes the scale so 1.0 = upper normal limit, making interpretation easier
Frequently Asked Questions
Is BMI accurate for everyone?
BMI is a useful screening tool but not a perfect measure. It does not distinguish between muscle and fat mass, so athletes and muscular individuals may have a high BMI despite low body fat. For a more complete picture, combine BMI with other measurements like waist circumference.
What is a healthy BMI?
According to the WHO, a BMI between 18.5 and 24.9 is considered normal weight for adults. A BMI below 18.5 is underweight, and 25-29.9 is overweight. Obesity starts at 30.
What is BMI Prime?
BMI Prime is your BMI divided by 25 (the upper limit of normal BMI). A BMI Prime of 1.0 means you are at the upper boundary of normal weight. Below 1.0 is underweight or normal; above 1.0 is overweight or obese.
Does BMI differ for men and women?
The BMI formula is the same for men and women. However, women typically have more body fat than men at the same BMI. Some health professionals adjust BMI interpretation based on sex.
Can children use this BMI calculator?
No — this calculator is for adults (18+). Children and teens need age- and sex-specific BMI percentile charts. Consult a pediatrician for children's BMI assessment.
What is the difference between BMI and body fat percentage?
BMI uses only height and weight to estimate body composition, while body fat percentage directly measures the proportion of fat in your body. A muscular athlete may have a high BMI (overweight category) but a low body fat percentage. Body fat percentage gives a more accurate picture of fitness.
How to lower your BMI safely and naturally?
Focus on a balanced diet with a moderate calorie deficit and regular physical activity. Aim for losing 1-2 pounds per week through sustainable changes like eating more vegetables, reducing processed foods, and exercising 150 minutes per week. Crash diets are counterproductive for long-term BMI management.
BMI vs waist-to-hip ratio — which is a better health indicator?
They measure different things. BMI measures overall weight relative to height, while waist-to-hip ratio measures fat distribution. A person with a normal BMI can still have a high waist-to-hip ratio if they carry excess abdominal fat. Using both together gives the most complete health picture.
What BMI is considered obese and what are the health risks?
A BMI of 30.0 or higher is classified as obese. Obesity is divided into Class I (30-34.9), Class II (35-39.9), and Class III (40+). Higher BMI classes carry increased risks for heart disease, type 2 diabetes, certain cancers, sleep apnea, and joint problems.
Does BMI work differently for different ethnicities?
Research shows that health risks associated with BMI can vary by ethnicity. For example, Asian populations may face increased health risks at lower BMI thresholds (overweight starting at 23 instead of 25). Some health organizations recommend ethnicity-specific BMI cutoffs for more accurate risk assessment.