Free BMI Calculator - Check Your Body Mass Index
Calculate your BMI instantly with height and weight. Best free BMI calculator 2025 - see your BMI category and understand what it means for your health.
Quick Answer
BMI (Body Mass Index) is calculated as: BMI = weight (kg) / height (m)². For pounds and inches: BMI = weight × 703 / height². A BMI of 18.5-24.9 is considered normal weight. Calculate your BMI instantly at practicalwebtools.com by entering your height and weight in metric or imperial units.
Key Facts about BMI Calculator:
- BMI formula: weight (kg) / height (m)² or weight (lb) × 703 / height (in)²
- Underweight: BMI < 18.5
- Normal weight: BMI 18.5-24.9
- Overweight: BMI 25-29.9
- Obese: BMI 30+
- BMI does not distinguish between muscle and fat
- BMI is a screening tool, not a diagnostic of health
Why Use Our BMI Calculator?
Understand your body mass index:
BMI Calculation
Calculate BMI from height and weight instantly.
Category Display
See where you fall: underweight to obese.
Unit Toggle
Switch between metric and imperial.
Healthy Range
See the healthy weight range for your height.
Instant Results
Get your BMI immediately.
100% Private
Your health data stays on your device.
How to BMI Calculator in 3 Easy Steps
Calculate your BMI:
Enter Height
Your height in feet/inches or cm.
Enter Weight
Your weight in pounds or kg.
Get Results
See BMI number and category.
Technical Overview: How BMI Calculator Works
BMI calculation uses the Quetelet index formula: BMI = mass (kg) / height (m)². For imperial units, the formula adjusts to BMI = mass (lb) × 703 / height (in)². The calculator converts between unit systems and categorizes results according to WHO guidelines. BMI provides a simple mass-to-height ratio but does not account for body composition, age, or fitness level.
Expert Tips for BMI Calculator
Best practices from professionals to get the most out of your conversion
- 1
BMI is most useful as a population screening tool, not individual diagnosis
- 2
Athletes with high muscle mass may have elevated BMI despite being healthy
- 3
Combine BMI with waist circumference for better health assessment
- 4
BMI categories may not apply equally to all ethnic groups
- 5
Track BMI trends over time rather than focusing on a single measurement
Common Mistakes to Avoid
Learn from others and avoid these frequent pitfalls when using bmi calculator
Treating BMI as a definitive measure of health
Not accounting for muscle mass in active individuals
Using adult BMI categories for children (use BMI percentile instead)
Ignoring other health markers like blood pressure and cholesterol
Obsessing over BMI numbers instead of overall health behaviors
Industry Statistics & Trends
Key data points about bmi calculator and file formats
42% of US adults are obese (BMI 30+)
Source: CDC 2024
73% of US adults are overweight or obese (BMI 25+)
Source: CDC 2024
BMI was developed in the 1830s by Adolphe Quetelet
Source: Medical History
A 5-point BMI increase raises mortality risk by 30%
Source: Lancet 2016
Know Your BMI
Quick health screening metric
Understand weight relative to height
Track changes over time
Starting point for health conversations
Common Use Cases for BMI Calculator
Useful for:
Frequently Asked Questions
Everything you need to know about our bmi calculator
How do I calculate my BMI?
Weight (kg) / height (m)² or use our calculator for instant results.
BMI = weight (kg) / height (m)². For US units: weight (lb) × 703 / height (in)². Or use our calculator - enter height and weight for instant results.
What is a healthy BMI?
18.5-24.9 is considered healthy; individual factors matter too.
WHO classifies 18.5-24.9 as normal/healthy BMI. Under 18.5 is underweight, 25-29.9 is overweight, 30+ is obese. Individual health varies beyond BMI.
Is BMI accurate?
Useful screening tool but has limitations - does not measure body composition.
BMI is useful for population screening but has limitations. It does not distinguish muscle from fat, varies by ethnicity, and does not account for fitness level. Use as one health indicator among many.
What should my BMI be?
18.5-24.9 is the normal range; focus on healthy behaviors overall.
Aim for BMI 18.5-24.9 (normal range). But optimal BMI depends on your body composition, age, and health factors. Focus on healthy behaviors, not just the number.
Does BMI apply to athletes?
BMI may overestimate fat in athletes - muscle is denser than fat.
Athletes with high muscle mass often have elevated BMI despite being healthy. Muscle weighs more than fat, so BMI may overestimate body fat in muscular individuals.
Still have questions? Try the tool yourself!
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