How to Calculate BMI: Formula, Chart & What Your Number Means

Body Mass Index (BMI) is one of the most commonly used health metrics. Here's everything you need to know about calculating and understanding your BMI.

What is BMI?

BMI is a measurement that uses your height and weight to estimate body fat and assess health risks.

Why BMI matters:

Quick health screening tool
Identifies weight categories
Assesses disease risk
Tracks progress over time

BMI Formula

Metric System (kg and meters)

BMI = weight (kg) / [height (m)]²

Example:

Weight: 70 kg
Height: 1.75 m
BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9

Imperial System (pounds and inches)

BMI = [weight (lbs) / height (inches)²] × 703

Example:

Weight: 154 lbs
Height: 69 inches (5'9")
BMI = (154 / 69²) × 703 = (154 / 4,761) × 703 = 22.7

Step-by-Step Calculation

Metric Example

Person: 80 kg, 1.80 m tall

Square your height: 1.80 × 1.80 = 3.24
Divide weight by height squared: 80 / 3.24 = 24.7
Result: BMI = 24.7 (Normal weight)

Imperial Example

Person: 165 lbs, 66 inches (5'6") tall

Square your height: 66 × 66 = 4,356
Divide weight by height squared: 165 / 4,356 = 0.0379
Multiply by 703: 0.0379 × 703 = 26.6
Result: BMI = 26.6 (Overweight)

BMI Categories

Adult BMI Chart

Underweight: BMI < 18.5

Health risks: Malnutrition, weak immune system, osteoporosis

Normal weight: BMI 18.5 - 24.9

Ideal range for most adults
Lowest health risks

Overweight: BMI 25.0 - 29.9

Increased health risks
May benefit from weight loss

Obese Class I: BMI 30.0 - 34.9

Moderate health risks
Weight loss recommended

Obese Class II: BMI 35.0 - 39.9

Serious health risks
Medical intervention may be needed

Obese Class III: BMI ≥ 40.0

Very serious health risks
Immediate medical attention recommended

BMI by Height Chart

For Quick Reference

Height 5'0" (152 cm):

Underweight: < 95 lbs
Normal: 95-127 lbs
Overweight: 128-152 lbs
Obese: > 153 lbs

Height 5'4" (163 cm):

Underweight: < 108 lbs
Normal: 108-145 lbs
Overweight: 146-173 lbs
Obese: > 174 lbs

Height 5'8" (173 cm):

Underweight: < 122 lbs
Normal: 122-163 lbs
Overweight: 164-196 lbs
Obese: > 197 lbs

Height 6'0" (183 cm):

Underweight: < 137 lbs
Normal: 137-184 lbs
Overweight: 185-220 lbs
Obese: > 221 lbs

Health Risks by BMI Category

Underweight (< 18.5)

Weakened immune system
Osteoporosis risk
Anemia
Fertility issues
Malnutrition

Normal Weight (18.5-24.9)

Lowest mortality risk
Reduced chronic disease risk
Better quality of life
Optimal range for most

Overweight (25.0-29.9)

Slightly elevated risks
Type 2 diabetes risk increases
Higher blood pressure
Joint stress

Obese (≥ 30.0)

Type 2 diabetes
Heart disease
Stroke
Certain cancers
Sleep apnea
Osteoarthritis
High blood pressure
High cholesterol

BMI Limitations

1. Doesn't Measure Body Composition

Muscle vs fat not distinguished
Bodybuilders may have high BMI but low body fat
Elderly may have normal BMI but high body fat

2. Age Not Considered

Older adults naturally have more body fat
Same BMI means different things at different ages

3. Gender Differences

Women typically have more body fat than men at same BMI
Different health implications

4. Ethnicity Variations

Asian populations: Health risks at lower BMI
Different body compositions across ethnicities
Some guidelines use modified thresholds

5. Doesn't Account for Distribution

Waist circumference matters
Apple vs pear body shape
Central obesity more dangerous

Better Alternatives to BMI

1. Body Fat Percentage

More accurate measure of health:

Men: 10-20% athletic, 14-24% fitness
Women: 18-28% athletic, 21-31% fitness

Use our Body Fat Calculator

2. Waist Circumference

Simple and effective:

Men: < 40 inches healthy
Women: < 35 inches healthy
Measures abdominal fat

3. Waist-to-Hip Ratio

Assesses fat distribution:

Men: < 0.90 low risk
Women: < 0.85 low risk

4. Waist-to-Height Ratio

Easy to remember:

Keep waist less than half your height
Waist should be < 50% of height

BMI for Special Populations

Children and Teens

Use BMI-for-age percentiles
Compare to same age/gender peers
Different interpretation than adults
Consult pediatrician

Pregnant Women

BMI not used during pregnancy
Pre-pregnancy BMI determines weight gain goals
Different guidelines apply

Athletes

BMI often misleading
High muscle mass = high BMI
Use body fat percentage instead
Focus on performance and health markers

Elderly (65+)

Slightly higher BMI may be protective
Some studies show 25-27 optimal
Focus on maintaining muscle mass

How to Use BMI Effectively

1. Starting Point Only

Use as initial screening
Don't rely on it alone
Consider other metrics

2. Track Trends

Monitor changes over time
More important than single number
Look for patterns

3. Combine with Other Measurements

Waist circumference
Body fat percentage
Blood pressure
Blood sugar
Cholesterol levels

4. Consider Your Situation

Age
Gender
Ethnicity
Activity level
Muscle mass

5. Consult Professionals

Doctor for interpretation
Consider medical history
Personalized assessment

Ideal Weight by Height

General Guidelines

Height 5'0": 95-127 lbs (BMI 18.5-24.9)
Height 5'2": 104-137 lbs
Height 5'4": 108-145 lbs
Height 5'6": 115-154 lbs
Height 5'8": 122-164 lbs
Height 5'10": 129-174 lbs
Height 6'0": 137-184 lbs
Height 6'2": 144-194 lbs

These are ranges for normal BMI (18.5-24.9).

How to Improve Your BMI

If Underweight

Eat more calories than you burn
Choose nutrient-dense foods
Strength training to build muscle
Eat more frequently
Consult doctor if unintentional

If Overweight/Obese

Create calorie deficit
Increase physical activity
Eat more protein and fiber
Strength train to preserve muscle
Be patient and consistent

Use our Calorie Calculator to find your needs.

BMI Calculation Tips

For Accurate Measurement

Weight yourself:

Same time of day
Minimal clothing
After bathroom, before eating
Use reliable scale

Measure height:

Stand straight, heels together
Look straight ahead
Measure against wall
Remove shoes

Common Mistakes

Wrong units - mixing metric and imperial
Rounding too early - use full numbers
Incorrect height - measure accurately
Clothed weight - remove heavy items
Time of day - weight fluctuates

When to See a Doctor

Seek medical advice if:

BMI under 18.5 or over 30
Rapid unexplained weight changes
Health symptoms appear
Concerned about weight
Planning major weight loss
Have existing health conditions

BMI and Disease Risk

Studies Show Correlations

Type 2 Diabetes:

Risk doubles at BMI 25-30
Risk increases 20x at BMI > 35

Heart Disease:

Risk increases 32% per 5 BMI units over 25

Stroke:

Each 5 BMI unit increase = 40% higher risk

Cancer:

Several cancers linked to obesity
Risk increases with higher BMI

Mortality:

J-shaped curve
Lowest risk at BMI 20-25
Increases both ends of spectrum

Calculate Your BMI Now

Our BMI Calculator provides:

Instant calculation
BMI category
Healthy weight range
Personalized recommendations
Track progress over time

BMI in Different Countries

Adjusted Thresholds for Asian Populations

Some countries use modified BMI cutoffs:

Asia-Pacific Guidelines:

Underweight: < 18.5
Normal: 18.5-23
Overweight: 23-27.5
Obese: > 27.5

Why? Asian populations have higher health risks at lower BMI levels.

Conclusion

BMI is a useful screening tool but not the complete picture. Use it as:

Starting point for health assessment
Way to track general trends
Combined with other measurements

Don't obsess over the number. Focus on:

Overall health and fitness
How you feel
Blood markers
Body composition
Sustainable healthy habits

Calculate your BMI: Free BMI Calculator

Related Tools

Body Fat Calculator - More accurate assessment
Calorie Calculator - Find your calorie needs
Ideal Weight Calculator - Target weight range