BMI Calculator

Calculate your Body Mass Index and understand your weight status


Calculate Your BMI

Enter your details to calculate your Body Mass Index

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Your BMI Result

Enter your details and click calculate to see your BMI

BMI Categories
Underweight < 18.5
Normal weight 18.5 – 24.9
Overweight 25 – 29.9
Obese ≥ 30
Smart Input Formats
Height Formats
175 cm 175cm 1.75 m 1.75m 5'9" 5'9 5 ft 9 in 5ft 9in 69 in 69" 175 (auto-detects as cm)
Weight Formats
70 kg 70kg 154 lbs 154lbs 154 lb 154 pounds 70 (auto-detects based on value)

What is BMI?

Body Mass Index (BMI) is a simple calculation using a person's height and weight. The formula is BMI = kg/m² where kg is a person's weight in kilograms and m² is their height in metres squared.

BMI is a useful measure of overweight and obesity. It is calculated the same way for both adults and children but is interpreted differently for children.

BMI Limitations

BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat mass, so athletes may have a high BMI despite being healthy.

Other factors like age, sex, ethnicity, and muscle mass can influence the relationship between BMI and body fat. Consult a healthcare provider for a complete assessment.

Features

Understanding Your Results

Make informed decisions about your health

Smart Input

Enter height and weight in any format - we auto-detect and convert

Any Unit System

Works with cm, m, ft, in, kg, lbs - mix and match freely

Weight Goals

See your healthy weight range based on your height

Visual Gauge

Easy-to-understand visual representation of BMI

Reference

BMI Chart for Adults

Quick reference table for Body Mass Index categories

BMI Range Category Health Risk Recommendation
Below 18.5 Underweight Malnutrition risk, osteoporosis, weakened immune system Consult a healthcare provider about healthy weight gain strategies
18.5 – 24.9 Normal Weight Lowest risk for weight-related health issues Maintain current lifestyle with balanced diet and regular exercise
25.0 – 29.9 Overweight Increased risk of heart disease, high blood pressure, type 2 diabetes Consider lifestyle modifications, increase physical activity
30.0 – 34.9 Obese Class I High risk of cardiovascular disease, diabetes, sleep apnea Seek medical advice for weight management program
35.0 – 39.9 Obese Class II Very high risk of serious health conditions Medical intervention recommended, consider specialist consultation
40.0 and above Obese Class III Extremely high risk, significantly reduced life expectancy Immediate medical attention required, bariatric surgery may be considered

Healthy Weight Ranges by Height

Find your healthy weight range based on your height (BMI 18.5-24.9)

5'0" (152 cm) 95 - 128 lbs (43 - 58 kg)
5'2" (157 cm) 101 - 136 lbs (46 - 62 kg)
5'4" (163 cm) 108 - 145 lbs (49 - 66 kg)
5'6" (168 cm) 115 - 154 lbs (52 - 70 kg)
5'8" (173 cm) 122 - 164 lbs (55 - 74 kg)
5'10" (178 cm) 129 - 174 lbs (59 - 79 kg)
6'0" (183 cm) 136 - 184 lbs (62 - 83 kg)
6'2" (188 cm) 144 - 194 lbs (65 - 88 kg)
Learn

How to Calculate BMI Manually

Understanding the BMI formula and calculation methods

Metric Formula

BMI = Weight (kg) ÷ Height² (m²)
Example Calculation:
  • Weight: 70 kg
  • Height: 1.75 m
  • Height²: 1.75 × 1.75 = 3.0625
  • BMI: 70 ÷ 3.0625 = 22.9

Result: Normal Weight

Imperial Formula

BMI = (Weight (lbs) ÷ Height² (in²)) × 703
Example Calculation:
  • Weight: 154 lbs
  • Height: 69 inches (5'9")
  • Height²: 69 × 69 = 4761
  • BMI: (154 ÷ 4761) × 703 = 22.7

Result: Normal Weight

Step-by-Step BMI Calculation Guide

1
Measure Your Height

Stand straight against a wall without shoes. Use a measuring tape or stadiometer. Record in meters (e.g., 1.75m) or feet and inches (e.g., 5'9").

2
Measure Your Weight

Use a calibrated scale, preferably in the morning before eating. Wear minimal clothing. Record in kilograms (e.g., 70kg) or pounds (e.g., 154 lbs).

3
Apply the Formula

Square your height (multiply by itself), then divide your weight by this number. For imperial units, multiply the result by 703.

4
Interpret Your Result

Compare your BMI to the standard categories: Under 18.5 (Underweight), 18.5-24.9 (Normal), 25-29.9 (Overweight), 40+ (Obese).

Special Cases

BMI for Different Age Groups & Populations

BMI interpretation varies across different demographics

Children & Teens (2-19)

For children and adolescents, BMI is calculated the same way but interpreted using age-and-sex-specific percentiles. A child's BMI is compared to other children of the same age and sex.

  • Underweight: Below 5th percentile
  • Healthy: 5th to 85th percentile
  • Overweight: 85th to 95th percentile
  • Obese: 95th percentile or above

Older Adults (65+)

Research suggests slightly higher BMI ranges may be protective for older adults. A BMI of 25-27 might be optimal for those over 65, providing reserves for illness recovery.

  • Muscle mass naturally decreases with age
  • Standard BMI may overestimate body fat
  • Waist circumference is also important
  • Consult geriatric specialists for guidance

Athletes & Bodybuilders

BMI doesn't distinguish between muscle and fat mass. Athletes with high muscle mass may have elevated BMI despite low body fat and excellent health markers.

  • Body fat percentage is more accurate
  • DEXA scans provide detailed analysis
  • Waist-to-hip ratio is useful
  • Athletic performance is a health indicator

Pregnant Women

BMI is used before pregnancy to assess healthy weight gain during pregnancy. Standard BMI categories don't apply during pregnancy due to natural weight changes.

  • Underweight BMI: Gain 28-40 lbs
  • Normal BMI: Gain 25-35 lbs
  • Overweight BMI: Gain 15-25 lbs
  • Obese BMI: Gain 11-20 lbs

Asian Populations

Studies show Asian populations may have higher health risks at lower BMI values. WHO recommends adjusted BMI categories for Asian populations.

  • Underweight: Below 18.5
  • Normal: 18.5 - 22.9
  • Overweight: 23 - 24.9
  • Obese: 25 and above

Medical Conditions

Certain conditions affect BMI interpretation. Edema, amputations, or muscle-wasting diseases require adjusted assessments by healthcare professionals.

  • Fluid retention affects weight
  • Sarcopenia alters body composition
  • Chronic illness impacts metabolism
  • Individual assessment is essential
Health

Health Risks Associated with Abnormal BMI

Understanding how BMI relates to various health conditions

Underweight Health Risks

Having a BMI below 18.5 can indicate malnutrition or underlying health issues:

  • Weakened Immune System: Increased susceptibility to infections and slower healing
  • Osteoporosis: Higher risk of bone fractures due to reduced bone density
  • Fertility Issues: Irregular menstrual cycles and reduced fertility in women
  • Anemia: Insufficient iron and vitamin intake leading to fatigue
  • Hair Loss: Nutritional deficiencies affecting hair and skin health
  • Developmental Issues: In children, can affect growth and cognitive development

Overweight & Obesity Health Risks

A BMI of 25 or higher increases the risk of numerous health conditions:

  • Type 2 Diabetes: Insulin resistance and blood sugar regulation problems
  • Cardiovascular Disease: Heart attack, stroke, and high blood pressure
  • Sleep Apnea: Breathing difficulties during sleep causing fatigue
  • Joint Problems: Osteoarthritis and chronic back pain from excess weight
  • Certain Cancers: Increased risk of breast, colon, and kidney cancers
  • Mental Health: Depression, anxiety, and reduced quality of life

Tips for Maintaining a Healthy BMI

Balanced Diet

Eat plenty of fruits, vegetables, whole grains, lean proteins, and healthy fats. Control portion sizes and limit processed foods.

Regular Exercise

Aim for at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous activity per week, plus strength training.

Quality Sleep

Get 7-9 hours of sleep per night. Poor sleep disrupts hormones that regulate appetite and metabolism.

Stay Hydrated

Drink plenty of water throughout the day. Sometimes thirst is mistaken for hunger, leading to overeating.

Manage Stress

Chronic stress can lead to emotional eating and weight gain. Practice relaxation techniques like meditation or yoga.

Track Progress

Regularly monitor your weight and BMI. Keep a food diary and set realistic, achievable health goals.

Comparison

BMI vs Other Body Composition Metrics

Understanding different ways to measure body composition and health

Metric What It Measures Pros Cons
BMI Weight relative to height Easy to calculate, widely used, good for population studies Doesn't distinguish muscle from fat, varies by ethnicity
Body Fat Percentage Proportion of fat to total body mass More accurate measure of body composition Requires special equipment, measurements can vary
Waist Circumference Abdominal fat distribution Good indicator of visceral fat and heart disease risk Doesn't account for overall body composition
Waist-to-Hip Ratio Fat distribution pattern Identifies apple vs pear body shapes, predicts health risks Doesn't measure total body fat
DEXA Scan Bone density, fat, and lean mass Most accurate body composition analysis Expensive, requires medical facility, radiation exposure

Waist Circumference Guidelines

Men
Low Risk < 94 cm (37 in)
Increased Risk 94-102 cm (37-40 in)
High Risk > 102 cm (40 in)
Women
Low Risk < 80 cm (31.5 in)
Increased Risk 80-88 cm (31.5-35 in)
High Risk > 88 cm (35 in)
FAQ

Frequently Asked Questions About BMI

Get answers to common questions about Body Mass Index

A healthy BMI for most adults falls between 18.5 and 24.9. This range is associated with the lowest risk of weight-related health problems. However, it's important to note that BMI is just one indicator of health, and factors like muscle mass, age, sex, and ethnicity can affect what's optimal for you. Athletes may have a higher BMI due to muscle mass, while older adults might benefit from a slightly higher BMI. Always consult with a healthcare provider for personalized advice.

BMI is a useful screening tool for population-level health assessments, but it has limitations for individuals. It doesn't differentiate between muscle, bone, and fat mass, so muscular individuals may be classified as overweight despite being healthy. It also doesn't account for fat distribution – belly fat is more dangerous than fat in other areas. For a complete health picture, BMI should be considered alongside waist circumference, body fat percentage, blood pressure, cholesterol levels, and other health markers.

The BMI calculation and categories are the same for both men and women. However, body composition naturally differs between sexes – women typically have more body fat than men at the same BMI. Men tend to carry excess weight around the abdomen (apple shape), while women often store fat in the hips and thighs (pear shape). Abdominal fat is more strongly linked to health risks, which is why waist circumference is an important additional measurement, especially for men.

BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s as part of his work on "social physics." He created the Quetelet Index (now called BMI) to measure the degree of obesity in the general population. The term "Body Mass Index" was coined by American physiologist Ancel Keys in 1972. It became widely adopted because it provides a simple, inexpensive way to assess weight status without requiring specialized equipment. Despite its limitations, it remains the most commonly used metric for classifying weight categories globally.

For most adults, checking BMI once every few months is sufficient unless you're actively trying to lose or gain weight. During weight management programs, weekly or bi-weekly checks can help track progress. However, don't obsess over daily fluctuations – body weight naturally varies by 1-3 kg daily due to water retention, food intake, and other factors. Focus on long-term trends rather than day-to-day changes. Children's BMI should be monitored at regular pediatric checkups to track healthy growth patterns.

Yes, it's possible to be "metabolically healthy" with a higher BMI. Some people with BMI in the overweight or even obese range have normal blood pressure, cholesterol, and blood sugar levels. This is sometimes called "metabolically healthy obesity." However, research suggests this healthy status may not persist long-term, and higher BMI still increases risk of joint problems, sleep apnea, and certain cancers. Conversely, people with normal BMI can be "metabolically unhealthy" if they have poor diet, lack exercise, or carry excess visceral fat.

BMI is a ratio of weight to height and doesn't measure body composition directly. Body fat percentage measures the actual proportion of your weight that's fat versus lean mass (muscle, bone, organs). A person with 30% body fat and someone with 15% body fat can have the same BMI if their weight and height are identical. Body fat percentage is measured using methods like skinfold calipers, bioelectrical impedance scales, DEXA scans, or hydrostatic weighing. Healthy body fat ranges are typically 10-20% for men and 18-28% for women.

To lower your BMI safely, aim for gradual weight loss of 0.5-1 kg (1-2 lbs) per week. Create a moderate calorie deficit through a combination of reduced food intake and increased physical activity. Focus on whole foods, lean proteins, vegetables, and whole grains while limiting processed foods, sugary drinks, and excessive portions. Incorporate both cardio exercise and strength training to preserve muscle mass. Get adequate sleep, manage stress, and stay hydrated. Avoid crash diets or extreme restrictions that can lead to muscle loss, nutritional deficiencies, and weight regain.

The BMI formula is the same for children (weight ÷ height²), but interpretation is different. Children's BMI is plotted on age-and-sex-specific growth charts to determine their percentile ranking. A child at the 50th percentile has a BMI equal to or greater than 50% of children their age and sex. Categories are: Underweight (below 5th percentile), Healthy (5th-85th), Overweight (85th-95th), and Obese (above 95th). This is because healthy body fat levels change as children grow, and boys and girls develop differently.

If your BMI is outside the normal range, don't panic – BMI is just one indicator. First, consider factors like muscle mass, age, and body type that might affect your reading. If you're genuinely underweight or overweight, consult a healthcare provider or registered dietitian for personalized guidance. They can assess your overall health, identify any underlying conditions, and develop a safe plan for reaching a healthy weight. Avoid self-prescribing extreme diets or supplements. Focus on sustainable lifestyle changes including balanced nutrition, regular physical activity, adequate sleep, and stress management.
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Medical Disclaimer

This BMI calculator is provided for informational and educational purposes only. It is not intended as a substitute for professional medical advice, diagnosis, or treatment. BMI is a screening tool and does not directly measure body fat or account for individual factors such as muscle mass, bone density, age, sex, ethnicity, or overall health status.

Always consult with a qualified healthcare provider before making decisions about your health, diet, or exercise regimen. If you have concerns about your weight or health, please seek guidance from a medical professional who can provide personalized recommendations based on a comprehensive evaluation of your individual circumstances.