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BMI Calculator.

Calculate Body Mass Index and health status

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Set your values

Results update as you type.

What is BMI?

Body Mass Index compares your weight to your height to give a single number that estimates whether your weight is in a healthy range. It is a quick screening tool, not a diagnosis.

Your BMI Results

Your BMI

22.9

Normal

Health risk: Low

1518.5253040

Ideal weight range

56.7 - 76.3 kg

Weight status

✓ In the ideal range

BMI Categories

Severe Thinness< 16.0
Moderate Thinness16.0 - 16.9
Mild Thinness17.0 - 18.4
Normal18.5 - 24.9
Overweight25.0 - 29.9
Obese Class I30.0 - 34.9
Obese Class II35.0 - 39.9
Obese Class III≥ 40.0
BMI Prime: 0.91

BMI Prime

0.91
Ponderal Index: 13.06

Ponderal Index

13.06
Body Surface Area: 1.85 m²

Body Surface Area

1.85 m²

Important Notes

  • BMI does not distinguish between fat, muscle, and bone mass.
  • Athletes and very muscular people often have a high BMI without excess fat.
  • It is less accurate for children, older adults, and people who are pregnant.
  • Waist circumference and body fat percentage add useful context to BMI.
  • Talk to a healthcare professional before making changes based on your BMI.

How to Use the BMI Calculator

  1. Choose your units. Switch between metric (kg and cm) and imperial (lbs and inches) to match how you normally measure.
  2. Enter your weight. Use your current weight, ideally measured in the morning before eating.
  3. Enter your height. Measure without shoes, standing straight with your heels together.
  4. Read your result. Your BMI, weight category, and ideal weight range update as you type.

Understanding Your BMI

BMI is calculated by dividing your weight in kilograms by the square of your height in metres. The result places you in one of five broad categories, from underweight through to obesity.

The categories come from population studies linking body weight to health outcomes. They describe trends across large groups, so an individual reading is a starting point for a conversation rather than a verdict on your health.

Because BMI only uses height and weight, it cannot tell muscle from fat or show where fat is stored. Two people with the same BMI can have very different body compositions, which is why measurements like waist circumference and body fat percentage are worth looking at alongside it.

Tips for Using BMI Well

  • Track the trend. A single reading says less than the direction your BMI moves over several months.
  • Measure consistently. Weigh yourself at the same time of day, on the same scale, in similar clothing.
  • Add a waist measurement. Waist circumference reflects where fat is stored, which BMI cannot capture.
  • Consider your build. Muscle is denser than fat, so a strength athlete may read as overweight while carrying little fat.
  • Look at the whole picture. Sleep, activity, blood pressure, and energy levels all say more about health than one number.
  • Get professional input. A doctor or dietitian can interpret your BMI in the context of your medical history.

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FAQs

What is BMI and how is it calculated?

BMI (Body Mass Index) is a measure of body fat based on height and weight. It is calculated using the formula: BMI = weight (kg) / [height (m)]². For imperial units: BMI = 703 × weight (lbs) / [height (inches)]².

What is a healthy BMI range?

A healthy BMI for adults is between 18.5 and 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is classified as obese.

Is BMI accurate for everyone?

BMI is a useful screening tool but has limitations. It may not be accurate for athletes with high muscle mass, pregnant women, elderly individuals, or children. Consult a healthcare professional for personalized assessment.

How often should I check my BMI?

For general health monitoring, checking BMI once a month is sufficient. If you are actively trying to gain or lose weight, weekly checks can help track progress.

Cite this calculator

Canonical URL: https://mathify.one/zh/fitness/bmi

Cite as: Mathify. (2026). BMI 计算器. https://mathify.one/zh/fitness/bmi

Use Cases

Health Screening

Quickly assess if your weight is in a healthy range for your height, helping you identify potential health risks associated with being underweight, overweight, or obese.

Example: A 30-year-old woman calculates her BMI to see if she's at risk for weight-related conditions.

Fitness Goal Setting

Use your BMI as a baseline to set realistic weight loss or gain goals, and track progress over time.

Example: A man aiming to lose weight checks his BMI monthly to monitor his progress.

Frequently Asked Questions

What is BMI and how is it calculated?
BMI, or Body Mass Index, is a number calculated from your weight and height. It's used to screen for weight categories that may lead to health problems. The formula is weight in kilograms divided by height in meters squared (kg/m²).
What BMI categories are there?
Standard BMI categories are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obesity (30 and above). These categories help assess if your weight is in a healthy range for your height.
Is BMI an accurate measure of body fat?
BMI is a useful screening tool but doesn't directly measure body fat. It may overestimate body fat in athletes or muscular individuals and underestimate it in older adults or those with less muscle. It's best used as a general indicator, not a diagnostic tool.

Tips & Common Mistakes

Tips

  • Use a reliable scale and measure your height accurately for the most precise BMI result.
  • For a more complete health picture, combine BMI with waist circumference and other health indicators.
  • Remember that BMI is a screening tool, not a diagnostic. Consult a healthcare professional for a full assessment.
  • Track your BMI over time to see trends, but don't obsess over small fluctuations.

Common Mistakes to Avoid

  • Entering weight in pounds instead of kilograms, or height in feet/inches instead of meters, leading to incorrect BMI.
  • Assuming BMI is a direct measure of body fat, ignoring muscle mass and distribution.
  • Using BMI as the sole determinant of health, without considering other factors like diet, exercise, and family history.

Last updated: August 13, 2026