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Calculators · Health & pregnancy

BMI calculator

Work out your Body Mass Index from height and weight, and see where it falls against the standard WHO adult categories.

Runs in your browser No signup Free forever Metric · US · UK units
Units

Enter your height and weight, then calculate — your BMI, category and healthy weight range will appear here.

0 kg/m²
—
Underweight Normal Overweight Obese
Healthy weight range
—
To reach normal BMI
—
BMI categories (WHO, adults)
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How it works

Three steps, no account

1

Pick your unit system

Metric (cm, kg), United States (feet/inches, pounds), or United Kingdom (feet/inches, stone and pounds).

2

Enter height and weight

Both fields are required — BMI is a ratio of the two, so a calculation needs both numbers to mean anything.

3

Read the breakdown

Your BMI, its category, where it sits on the scale, and the weight range that would put you in the "normal" band.

FAQ

Common questions

Is BMI accurate for everyone?
No single number is. BMI doesn't separate muscle from fat, so it tends to overestimate body fat in athletes and very muscular people, and can underestimate it in older adults who've lost muscle mass. It's a useful population-level screening tool, not an individual diagnosis.
Does my height and weight get sent anywhere?
No. The calculation runs entirely in your browser with plain JavaScript — nothing is transmitted, logged, or stored anywhere.
Why does the UK option ask for stone and pounds?
Stone remains the everyday unit for body weight in the UK and Ireland, even though most other measurements are metric. Height still uses feet and inches for the same reason — the calculator matches how people actually think about their own numbers.
Is a different BMI range used for children?
Yes — children and teenagers are assessed against age- and sex-specific percentile charts, not the fixed adult thresholds this calculator uses. This tool is intended for adults aged 18 and over.
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BMI Calculator

Our BMI Calculator provides a quick and easy way to calculate your Body Mass Index (BMI) and determine your weight category. Use this tool to assess whether you are underweight, normal weight, overweight, or obese.

How to Use the BMI Calculator

1. Select Your Unit System

  • Choose between Metric, United States, or United Kingdom units
  • The calculator will adjust input fields based on your selection

2. Enter Your Height

  • Metric: Enter your height in centimeters
  • US/UK: Enter your height in feet and inches

3. Enter Your Weight

  • Metric: Enter your weight in kilograms
  • US: Enter your weight in pounds
  • UK: Enter your weight in stones and pounds

4. Calculate Your BMI

  • Click the "Calculate" button
  • Your BMI value and weight category will be displayed instantly

BMI Categories

  • Underweight: BMI below 18.5
  • Normal Weight: BMI between 18.5 and 24.9
  • Overweight: BMI between 25.0 and 29.9
  • Obese: BMI 30.0 and above

Use Cases

1. Personal Health Assessment

  • Monitor your weight category over time
  • Set weight management goals
  • Track progress in fitness programs

2. Healthcare and Fitness

  • Assess patient weight categories
  • Provide personalized health advice
  • Integrate into fitness apps and programs

3. Educational Purposes

  • Teach students about BMI and health
  • Demonstrate the impact of weight on health
  • Use in health and fitness courses

Technical Features

  • Dynamic Input Fields: Adjusts based on selected unit system
  • Real-Time Calculation: Instant results upon input
  • Responsive Design: Works on mobile, tablet, and desktop devices
  • BMI Categories Reference: Easy-to-read table for quick assessment
  • No Data Storage: All calculations performed locally in your browser

Why Use Our BMI Calculator

1. Accurate and Reliable

  • Uses standard BMI formula
  • Provides precise results with one decimal point

2. User-Friendly Interface

  • Simple and intuitive design
  • Clear instructions and labels
  • Instant feedback with color-coded categories

3. Privacy Focused

  • No personal data collection
  • Works offline after initial page load
  • Safe and secure for all users

Understanding BMI

What is BMI?

BMI is a measure of body fat based on height and weight. It is used to categorize individuals into weight categories that may indicate potential health risks.

How is BMI Calculated?

BMI is calculated by dividing a person's weight in kilograms by the square of their height in meters. For imperial units, the formula is adjusted to account for pounds and inches.

Limitations of BMI

While BMI is a useful screening tool, it does not directly measure body fat or account for muscle mass, bone density, or distribution of fat. It should be used alongside other assessments for a comprehensive health evaluation.

Remember: Always consult with a healthcare professional for personalized health advice and before making significant changes to your diet or exercise routine.