BMI Calculator

Calculate your Body Mass Index instantly. Free BMI calculator with health category assessment, body fat estimation, ideal weight range, and comprehensive health analysis. Complete health assessment tool for weight management.

Measurement System

Choose between metric or imperial units

Weight (kg)

Enter your current weight

Height (cm)

Enter your height

Age (years) - Optional

For more accurate body fat estimation

Gender - Optional

For more accurate body fat estimation

Enter your details and click "Calculate BMI" to see results.

Health Assessment Results

BMI Score

0.0

Body Mass Index

How to Use Our BMI Calculator

Select Measurement System: Choose between Metric (kg/cm) or Imperial (lbs/feet) units
Enter Your Weight: Input your current weight in the selected unit system
Enter Your Height: Input your height in the selected unit system
Optional Details: Add age and gender for more accurate body fat estimation
Calculate BMI: Click "Calculate BMI" to see your BMI score and health analysis
Analyze Results: Review your BMI category, body fat estimation, and ideal weight range
Copy Results: Use "Copy Results" to copy calculations to clipboard
Export Results: Use "Export to Excel" to download your calculation
Reset Tool: Use "Reset" button to clear all fields

Understanding BMI Calculations: The Mathematical Formula

BMI calculations use a simple mathematical formula that relates weight to height. Here's the exact mathematical formula our calculator uses:

BMI Calculation Formula:

Metric: BMI = weight (kg) ÷ [height (m)]²

Imperial: BMI = [weight (lbs) ÷ [height (in)]²] × 703

Where:

BMI = Body Mass Index (kg/m²)
Weight = Your body weight in kilograms or pounds
Height = Your height in meters or inches

The formula provides a standardized measure that allows comparison across different populations.

Pro Tip: The multiplier 703 in the imperial formula converts the result to the same scale as the metric formula, allowing consistent interpretation.

Real Example Calculation:

Let's calculate BMI for a person who weighs 70 kg and is 175 cm tall:

Convert height to meters: 175 cm = 1.75 m
Calculate height squared: 1.75 × 1.75 = 3.0625 m²
Divide weight by height squared: 70 ÷ 3.0625 = 22.86
Result: BMI = 22.86 (Normal weight category)

BMI Categories and Health Risks

BMI Category	BMI Range	Health Risks	Recommended Action
Underweight	< 18.5	Nutritional deficiencies, osteoporosis, weakened immunity	Increase calorie intake, strength training
Normal Weight	18.5-24.9	Lowest health risks, optimal health	Maintain current lifestyle
Overweight	25-29.9	Increased risk of hypertension, type 2 diabetes, heart disease	Moderate weight loss, increased activity
Obese Class I	30-34.9	High risk of cardiovascular diseases, metabolic syndrome	Structured weight loss program
Obese Class II	35-39.9	Very high risk, sleep apnea, joint problems	Medical supervision recommended
Obese Class III	≥ 40	Extremely high risk, reduced life expectancy	Immediate medical intervention

Statistical Insight: Each 5-point increase in BMI above 25 is associated with approximately 30% higher mortality risk from cardiovascular causes.

Body Fat Percentage Estimation

BMI provides an indirect measure of body fat. We estimate body fat percentage using established formulas:

Body Fat Estimation Formulas:

For Adult Men: Body Fat % = (1.20 × BMI) + (0.23 × Age) - 16.2

For Adult Women: Body Fat % = (1.20 × BMI) + (0.23 × Age) - 5.4

These formulas are based on large population studies and provide reasonable estimates for most adults.

Category	Men (Body Fat %)	Women (Body Fat %)	Health Implications
Essential Fat	2-5%	10-13%	Minimum required for physiological functions
Athletes	6-13%	14-20%	Optimal for sports performance
Fitness	14-17%	21-24%	Good health and fitness level
Average	18-24%	25-31%	Acceptable range for general health
Overweight	25%+	32%+	Increased health risks
Obese	30%+	37%+	High health risk category

Ideal Weight Range Calculation

Your ideal weight range is calculated based on the healthy BMI range (18.5-24.9) for your height:

Ideal Weight Formulas:

Metric: Min Weight = 18.5 × [height (m)]²

Metric: Max Weight = 24.9 × [height (m)]²

Imperial: Min Weight = [18.5 × height² (in)] ÷ 703

Imperial: Max Weight = [24.9 × height² (in)] ÷ 703

Why Ideal Weight Matters

The ideal weight range represents weights associated with the lowest health risks. Being within this range reduces your risk of weight-related health problems by 50-70% compared to being overweight or obese.

Realistic Weight Goals

Our calculator provides a realistic range rather than a single number. This accounts for natural variations in body composition and helps set achievable, healthy weight goals.

Limitations of BMI: What It Doesn't Tell You

While BMI is a useful screening tool, it has important limitations:

Muscle Mass vs Fat Mass

BMI doesn't distinguish between muscle and fat. Athletes and bodybuilders may have high BMI due to muscle mass, not excess fat.

Body Composition Differences

BMI doesn't account for fat distribution (apple vs pear shape), bone density, or ethnic variations in body composition.

Age-Related Changes

BMI may overestimate body fat in older adults who have lost muscle mass (sarcopenia) but maintained weight.

Important: BMI should be used as a screening tool, not a diagnostic tool. Always consult with healthcare professionals for comprehensive health assessment.

Evidence-Based Strategies for BMI Improvement

Based on your BMI category, here are evidence-based strategies for improvement:

BMI Category	Nutrition Strategy	Exercise Strategy	Weekly Goal
Underweight	Calorie surplus, protein-rich foods	Strength training 3× week	Gain 0.5-1 lb (0.2-0.5 kg)
Normal Weight	Balanced maintenance	Mix of cardio & strength	Maintain weight ±2 lbs
Overweight	500-calorie daily deficit	150 mins moderate cardio	Lose 1-2 lbs (0.5-1 kg)
Obese Class I	750-calorie daily deficit	200 mins cardio + strength	Lose 1-2 lbs (0.5-1 kg)
Obese Class II/III	Medical supervision	Supervised exercise	Lose 1-2 lbs (0.5-1 kg)

Success Tip: Sustainable weight loss is 1-2 pounds (0.5-1 kg) per week. Rapid weight loss often leads to muscle loss and weight regain.

Why Use Our BMI Calculator?

Accurate Calculations

Uses standard WHO formulas for precise BMI calculation with both metric and imperial units support.

Body Fat Estimation

Estimates body fat percentage based on BMI, age, and gender for comprehensive health assessment.

Export to Excel

Download your BMI calculations as CSV files for tracking progress and medical record keeping.

Frequently Asked Questions

What is BMI and how is it calculated?

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

Is BMI an accurate measure of health?

BMI is a useful screening tool but has limitations. It doesn't account for muscle mass, bone density, or fat distribution. For a complete health assessment, consult with a healthcare professional.

What are the standard BMI categories?

The standard categories are: Underweight (BMI < 18.5), Normal weight (18.5-24.9), Overweight (25-29.9), and Obesity (30 or higher).

Can I use this calculator for children?

This calculator is designed for adults (ages 20+). Children and teenagers require age and gender-specific BMI percentiles for accurate assessment.

How do I calculate body fat percentage from BMI?

Body fat percentage can be estimated from BMI using age and gender factors. Our calculator provides this estimation based on established health formulas.

How accurate is the body fat percentage estimation?

Body fat percentage estimation from BMI is an approximation based on population studies. For the most accurate measurement, methods like DEXA scans, bioelectrical impedance analysis, or skinfold measurements are recommended.

What is the ideal weight range calculation based on?

The ideal weight range is calculated based on the healthy BMI range (18.5-24.9) for your height. It provides a target weight range for optimal health.

How often should I check my BMI?

For most adults, checking BMI every 1-3 months is sufficient for monitoring weight changes. More frequent checking may be needed during active weight management programs.

Comprehensive Health Assessment with BMI

Our free online BMI Calculator provides more than just a number - it offers comprehensive health insights:

Health Risk Assessment

Identify potential health risks based on your BMI category and get personalized recommendations for improvement.

Progress Tracking

Use our export feature to track BMI changes over time and monitor the effectiveness of your health interventions.

Goal Setting

Set realistic weight goals based on your ideal weight range and track progress toward achieving a healthy BMI.

BMI is particularly useful for population-level health assessment and individual screening. When combined with other health indicators like waist circumference, blood pressure, and cholesterol levels, BMI provides valuable insights into overall health status.

With support for both metric and imperial units, you can calculate BMI regardless of your preferred measurement system. The calculator also allows you to export results to Excel for further analysis and medical record keeping.