BMI Calculator
Calculate your Body Mass Index (BMI) using height and weight. Supports both metric and imperial units. Includes BMI chart and health classification.
Your BMI
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BMI Categories (WHO)
Underweight < 18.5
Normal weight 18.5 โ 24.9
Overweight 25.0 โ 29.9
Obese Class I 30.0 โ 34.9
Obese Class II 35.0 โ 39.9
Obese Class III โฅ 40.0
BMI Formula
BMI = weight (kg) / heightยฒ (m) Imperial: BMI = 703 ร weight (lb) / heightยฒ (in)
Frequently Asked Questions
- BMI = weight (kg) รท heightยฒ (mยฒ). Example: 70 kg รท (1.75m ร 1.75m) = 22.9. In imperial units: BMI = 703 ร weight (lbs) รท heightยฒ (inchesยฒ). A BMI of 18.5โ24.9 is considered normal weight.
- The BMI formula is the same for men and women. However, the interpretation differs slightly โ women naturally carry more body fat than men at the same BMI. Some health professionals use adjusted ranges: a BMI of 21โ23 is considered optimal for women; 22โ24 for men. Athletes may also have elevated BMI due to muscle mass.
- According to the WHO: Under 18.5 = Underweight; 18.5โ24.9 = Normal weight; 25.0โ29.9 = Overweight; 30.0+ = Obese. The ideal BMI range for most adults is 20โ25. For adults over 65, a slightly higher BMI (25โ27) may be protective.
- No โ BMI is not accurate for people with high muscle mass. Muscle weighs more than fat, so athletes often have a 'overweight' or 'obese' BMI despite having low body fat. Better measures for athletes include body fat percentage, waist-to-hip ratio, or DEXA scans.
- The most common methods: Skinfold calipers (measures skin folds at multiple sites); Bioelectrical impedance (sends a small current through the body); Navy method (uses neck and waist measurements); DEXA scan (most accurate, medical-grade). Healthy body fat: men 10โ20%, women 18โ28%.
- A BMI of 30 or above is classified as obese. Obesity is further categorized: Class I (30โ34.9), Class II (35โ39.9), and Class III or 'severe obesity' (40+). Obesity is associated with increased risk of type 2 diabetes, heart disease, high blood pressure, and certain cancers.
- BMI uses the same formula for all adults, but interpretation changes with age. For children and teens, BMI is age- and sex-specific (called BMI-for-age percentile). For older adults (65+), a BMI of 25โ27 may actually be associated with better health outcomes than a 'normal' BMI.
- To reduce BMI, you need to lose body fat through a combination of: caloric deficit (eating fewer calories than you burn), regular aerobic exercise (150+ minutes/week), and strength training (builds muscle, increases metabolism). A safe rate of weight loss is 0.5โ1 kg (1โ2 lbs) per week.
- BMI does not account for: muscle vs. fat distribution, bone density, age, sex, or ethnicity. It also doesn't measure where fat is stored โ visceral fat (around organs) is more dangerous than subcutaneous fat. BMI is a useful population-level screening tool but should be combined with other assessments for individual health evaluation.