- Free Health Tool
BMI Calculator
A simple, accurate BMI calculator that estimates your Body Mass Index from height and weight, with full support for metric and imperial units.
Use our BMI calculator to check your Body Mass Index using height and weight, with metric and imperial units.
- Free online BMI calculator for adults, men and women.
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What Is a BMI Calculator?
A BMI calculator estimates your Body Mass Index using your height and weight. It helps adults understand whether their weight falls into underweight, healthy weight, overweight, or obesity categories. This online BMI calculator works for men and women and supports metric and imperial units.
How the BMI Calculator Works
Pick metric (kg, cm) or imperial (lbs, inches). The BMI calculator handles both.
Choose Your Unit System
Pick metric (kg, cm) or imperial (lbs, inches). The BMI calculator handles both.
Enter Height & Weight
Type in your height and weight, the two values needed to calculate BMI accurately.
Add Age & Gender
Optionally include age and gender for added context, the BMI formula stays the same.
View Your Result
Instantly see your BMI score, category, and healthy weight range for your height.
How to Use This BMI Calculator
Follow these six simple steps to calculate your BMI and read your result with confidence.
Select Units
Choose Metric or Imperial depending on your preference
Enter Your Weight
Type your weight in kilograms or pounds.
Enter Your Height
Add your height in centimetres, metres, feet, or inches.
Add Age & Gender
Optional fields for added context, not required for the BMI formula.
Click Calculate BMI
Add pregnancy, breastfeeding, illness, or diet factors.
Review Your Result
Read your BMI category and healthy weight range for your height.
How Is BMI Calculated?
BMI is calculated using a simple mathematical formula that relates your weight to your height. Here’s how it works in both metric and imperial units.
Metric BMI Formula
When using kilograms and metres:
Imperial BMI Formula
When using pounds and inches:
Worked Example
If someone weighs 75 kg and is 1.75 m tall:
A BMI of 24.5 falls into the healthy weight range for adults.
This is exactly how BMI is calculated by health organisations worldwide. Our calculator runs the same BMI calculation formula automatically, you only need to enter your height and weight.
BMI Categories Explained
BMI results fall into four standard categories for adults aged 18 and over.
Underweight
Healthy Weight
Overweight
Obesity
Note: BMI is a screening tool, not a medical diagnosis. Always speak to a healthcare professional for personal advice.
BMI Calculator for Men and Women
How the BMI calculator works for both sexes, and what you should know before interpreting your number.
BMI Calculator for Men
- The male BMI calculator uses the exact same formula as the female version.
- Men typically have lower body fat and more lean muscle than women at the same BMI.
- Highly muscular men, bodybuilders, rugby players, strength athletes, often score in the overweight range despite low body fat.
- For most adult men, BMI remains a reliable quick health screening number.
BMI Calculator for Women
- The female BMI calculator uses the standard BMI formula without adjustment.
- Women generally carry more body fat than men at the same BMI, this is normal and healthy.
- Pregnant women should not rely on BMI; pregnancy-specific guidance from a clinician is more appropriate.
- Hormonal changes, menopause, and post-pregnancy recovery can affect body composition independently of BMI.
In short, the BMI calculator for women and the BMI calculator for men use the same formula, but body composition, age, and muscle mass should always be considered alongside the result.
Why Use Our Online BMI Calculator?
Six reasons our BMI calculator stands out from the rest.
Quick BMI Result
Get your Body Mass Index in under five seconds.
Metric & Imperial Support
Calculate BMI in kg and cm or in pounds and inches.
Healthy Weight Range
See the recommended weight range for your height.
PDF Result Download
Save your BMI report as a PDF for future reference.
Built for Men & Women
Simple, accurate, and inclusive for all adult users.
Mobile-Friendly Tool
Use the BMI calculator smoothly on phone, tablet, or desktop.
Common BMI Mistakes to Avoid
Avoid these frequent errors when using a BMI calculator so your result reflects reality.
- Using Wrong Height Units
Mixing centimetres with metres, or feet with inches, produces a wildly inaccurate BMI. Double-check your input unit before calculating.
- Confusing Pounds & Kilograms
Entering pounds into a metric field (or vice versa) skews your BMI by more than 2x. Always select the matching unit system first.
- Treating BMI as a Diagnosis
BMI is a screening number, not a medical verdict. A “high” BMI alone does not mean you are unhealthy, context matters.
- Ignoring Muscle Mass
Muscular athletes often score in the overweight range despite excellent health. BMI cannot distinguish lean muscle from body fat.
- Comparing Adult BMI to Children
Children and teenagers need age- and sex-specific BMI-for-age percentiles, not the standard adult BMI calculator.
- Not Speaking to a Professional
If your BMI result concerns you, consult a doctor or registered dietitian rather than relying on online tools alone.
Frequently Asked Questions
Quick, clear answers to the most common questions about BMI calculators and how BMI is calculated.
What is a BMI calculator?
A BMI calculator is an online tool that estimates your Body Mass Index from your height and weight. It places adults into underweight, healthy weight, overweight, or obesity categories and works for both men and women.
How do I calculate my BMI?
To calculate your BMI, divide your weight in kilograms by your height in metres squared. For example, 75 kg ÷ (1.75 m × 1.75 m) = 24.5. Our calculator does this automatically in metric or imperial units.
What is the BMI calculation formula?
The metric BMI formula is BMI = weight (kg) ÷ height (m)². The imperial BMI formula is BMI = 703 × weight (lbs) ÷ height (inches)². Both produce the same final result.
How do you calculate BMI in kg and cm?
Convert your height from centimetres to metres by dividing by 100, then square that number. Divide your weight in kilograms by the squared height. Example: 70 kg ÷ (1.70 × 1.70) = 24.2 BMI.
How do you calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. Example: (165 × 703) ÷ (68 × 68) = 25.1 BMI.
Is BMI calculator accurate?
A BMI calculator is accurate as a general screening tool for most adults, but it does not measure body fat directly. It may be less accurate for athletes, pregnant people, older adults, children, or anyone with high muscle mass.
Is BMI different for men and women?
The BMI formula is the same for men and women. However, body composition naturally differs — women typically carry more body fat than men at the same BMI — so context matters when interpreting the result.
What is a healthy BMI range?
A healthy BMI range for most adults is between 18.5 and 24.9. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classed as obesity.
Can athletes use a BMI calculator?
Athletes can use a BMI calculator, but the result is often misleading. Muscle weighs more than fat, so muscular athletes frequently fall into the overweight category despite having very low body fat.
Is BMI calculator suitable for children?
This BMI calculator is designed for adults aged 18 and over. Children and teenagers should use BMI-for-age percentile charts instead, which account for growth and development.
What does BMI calculate?
BMI calculates the ratio of your weight to your height. It indicates whether your weight is appropriate for your height but does not measure body composition, fat distribution, or overall health.
Can BMI tell me my body fat percentage?
No. BMI does not measure body fat percentage. For an accurate body fat reading, use methods such as DEXA scans, skinfold callipers, bioelectrical impedance, or hydrostatic weighing.
Calculate Your BMI in Seconds
Use the free Imperial Fitness Hub BMI Calculator to estimate your Body Mass Index and understand your healthy weight range.
Disclaimer: This BMI calculator is for general information only and is not medical advice. BMI does not directly measure body fat and may not be accurate for athletes, pregnant people, children, older adults, or people with high muscle mass. Speak with a qualified healthcare professional for personal advice.
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