BMI Calculator (Body Mass Index)
Calculate your body mass index (BMI) instantly. Supports metric (kg/cm), imperial (lbs/ft), and UK stone/lbs units. Includes official BMI chart for men and women, formula breakdown, and pediatric guidelines.
Medical Disclaimer: BMI is a screening estimate only — not a medical diagnosis. It does not account for muscle mass, bone density, ethnicity, or age. Consult a qualified healthcare professional for a complete health assessment. Full disclaimer →
fFormula & How It's Calculated
Example (metric): 70 kg ÷ (1.75 m)² = 70 ÷ 3.0625 = BMI 22.86 (Normal weight)
Frequently Asked Questions (FAQ)
How do I calculate BMI formula for men and women?
The BMI formula is the same for men and women. In metric units: BMI = weight(kg) ÷ [height(m)]². In imperial: BMI = 703 × weight(lbs) ÷ [height(in)]². For example, a 70 kg person 1.75 m tall has a BMI of 22.9.
What is a normal BMI for women?
A healthy BMI for adult women is 18.5 to 24.9. Below 18.5 is considered underweight, 25–29.9 overweight, and 30+ falls in the obese category per WHO guidelines.
What is a healthy BMI for men?
The healthy BMI range for adult men is 18.5 to 24.9 — identical to the overall adult standard. Because men tend to have higher muscle mass, BMI may slightly underestimate body fat. Consider waist circumference and body fat percentage for a complete picture.
How does the BMI calculator for teens work?
For teens aged 2–19, BMI is calculated the same way but interpreted using CDC age- and sex-specific percentile charts. A BMI between the 5th and 85th percentile is healthy. This tool is designed for adults (20+). Always consult a paediatrician for children and adolescents.
What is a normal BMI?
A normal BMI ranges from 18.5 to 24.9 for adults. This range indicates a healthy weight relative to height and is associated with the lowest risk of weight-related health problems.
Is BMI accurate for all body types?
BMI is a useful screening tool but does not directly measure body fat. It may overestimate risk in athletes with high muscle mass and underestimate it in older adults with low muscle. Use BMI alongside waist circumference and professional health advice.
Complete Adult BMI Chart for Men and Women
The following body mass index chart uses WHO standard classifications. These ranges apply to adults aged 20 and over, regardless of sex or ethnicity — though some health authorities recommend lower cut-offs for Asian populations.
| BMI Range | Weight Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese Class I |
| 35.0 – 39.9 | Obese Class II |
| 40.0 and above | Obese Class III |
Source: World Health Organization (WHO) Global BMI classification.
How to Calculate BMI Formula — Step-by-Step Guide
The calculate BMI formula divides body weight by the square of height. Here are step-by-step examples for both unit systems:
Metric Formula
- Convert height to metres (e.g., 175 cm = 1.75 m)
- Square the height: 1.75² = 3.0625
- Divide weight by result: 70 kg ÷ 3.0625 = 22.86
Imperial Formula
- Convert height to inches (5′9″ = 69 in)
- Square the height: 69² = 4761
- Calculate: 703 × 160 lbs ÷ 4761 = 23.6
BMI Calculator for Teens and Children: Percentile Scoring
For children and teenagers aged 2–19, BMI is interpreted differently using CDC percentile charts that account for age and biological sex. Unlike the standard adult BMI chart, a teen's BMI result must be compared against peers of the same age and sex.
| Percentile Range | Weight Status |
|---|---|
| Below the 5th | Underweight |
| 5th to below 85th | Healthy weight |
| 85th to below 95th | Overweight |
| 95th or above | Obese |
Source: U.S. Centers for Disease Control and Prevention (CDC).
Clinical Limitations of BMI as a Health Metric
While Body Mass Index is widely used by epidemiologists and health organisations as an inexpensive population screening tool, it has notable physiological limitations when applied to individual health assessments:
Muscle Mass vs. Adipose Tissue
BMI cannot differentiate between skeletal muscle mass and body fat. Athletes, bodybuilders, and strength trainers may register as "overweight" or "obese" despite having optimal metabolic health and low body fat percentages.
Visceral vs. Subcutaneous Fat Distribution
BMI calculates total mass relative to height, but cannot detect where fat is stored. Visceral fat surrounding abdominal organs carries significantly higher cardiometabolic and type 2 diabetes risk than subcutaneous fat on the hips and thighs.
Age-Related Muscle Loss (Sarcopenia)
As adults age, natural loss of lean muscle (sarcopenia) often masks increases in visceral body fat. An elderly individual may have a "normal" BMI yet possess unhealthy body composition (sarcopenic obesity).
Pregnancy and Postpartum Changes
Standard adult BMI classification charts are not valid for pregnant or breastfeeding individuals, whose weight fluctuations reflect fetal growth, amniotic fluid, and increased blood volume rather than metabolic adiposity.
WHO Asian Population Action Points (WHO Expert Consultation)
According to the World Health Organization (WHO) expert consultation published in The Lancet, individuals of Asian descent often face elevated risks of cardiovascular disease and type 2 diabetes at lower BMI thresholds than the standard international cutoffs:
Source: WHO Expert Consultation, Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies, The Lancet.
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