BMI Calculator
Calculate your Body Mass Index instantly using our BMI Calculator. Enter your height and weight in either metric or imperial units, and get immediate results showing your BMI score along with your weight category according to WHO standards. The calculator helps you understand whether you're underweight, normal weight, overweight, or obese, providing valuable insights for health and fitness tracking. Perfect for anyone monitoring their weight, setting fitness goals, or working with healthcare providers. The tool uses the standard BMI formula (weight in kg / height in m²) trusted by medical professionals worldwide. All calculations happen instantly in your browser with complete privacy—no data is stored or transmitted. Switch easily between kilograms/centimeters and pounds/inches to match your preference.
How it works: BMI (Body Mass Index) is calculated with the formula weight(kg) / height(m)². It is a screening tool for weight-category context, not a full body-composition or medical diagnosis.
What Is a BMI Calculator?
A BMI (Body Mass Index) calculator measures the ratio of your weight to your height squared. The formula is: BMI = weight (kg) / height (m)². For a 5'9" person (175 cm) weighing 180 lbs (82 kg): BMI = 82 / (1.75)² = 26.8 — placing them in the Overweight category. BMI is a population-level screening tool used by the CDC and WHO to classify weight-related health risk. It doesn't directly measure body fat, but correlates well with metabolic disease risk across large populations.
BMI Categories (WHO Standard)
| BMI Range | Category | Health Risk | Action |
|---|---|---|---|
| Below 18.5 | Underweight | Increased risk | Consult provider |
| 18.5 – 24.9 | Healthy Weight | Lowest risk | Maintain weight |
| 25.0 – 29.9 | Overweight | Moderate risk | Weight management |
| 30.0 – 34.9 | Obese Class I | High risk | Weight loss recommended |
| 35.0 – 39.9 | Obese Class II | Very high risk | Medical support advised |
| 40+ | Obese Class III | Extremely high risk | Immediate medical care |
For children and teens, BMI is interpreted using age- and sex-specific growth percentiles, not these adult categories.
Healthy Weight Range by Height
| Height | Healthy Min (BMI 18.5) | Healthy Max (BMI 24.9) | Overweight starts at | Obese starts at |
|---|---|---|---|---|
| 5'0" (152 cm) | 86 lbs | 115 lbs | 116 lbs | 139 lbs |
| 5'4" (163 cm) | 108 lbs | 145 lbs | 146 lbs | 175 lbs |
| 5'6" (168 cm) | 115 lbs | 155 lbs | 156 lbs | 186 lbs |
| 5'8" (173 cm) | 122 lbs | 164 lbs | 165 lbs | 197 lbs |
| 5'10" (178 cm) | 129 lbs | 173 lbs | 174 lbs | 209 lbs |
| 6'0" (183 cm) | 137 lbs | 184 lbs | 185 lbs | 221 lbs |
| 6'2" (188 cm) | 145 lbs | 194 lbs | 195 lbs | 234 lbs |
Worked Example: Alex at 5'9", 180 lbs
BMI = 82 kg / (1.75 m)² = 26.8 — Overweight
Healthy weight range at 5'9": 125–168 lbs | To reach healthy BMI, lose 12+ lbs
Body fat % (US Navy estimate): ~19% — in “Fit” range despite Overweight BMI
This illustrates why BMI should be used alongside body fat % and waist measurements
BMI Limitations
BMI doesn't distinguish between fat and muscle. A 200 lb athlete with 8% body fat will be classified as Overweight; a 150 lb sedentary person with 32% body fat may register as Normal. Asian populations face higher metabolic risk at lower BMI (around 23), so some clinicians use adjusted cutoffs. Women naturally carry more essential fat (10–13%) than men (2–5%), but BMI doesn't adjust for sex beyond the formula. Use BMI as a starting point, not the final word — pair it with waist circumference (<35" women, <40" men for low risk) and body fat % for a more complete picture.
Tips for Managing Your BMI
If your BMI is in the Overweight range: a 5–10% weight loss meaningfully reduces cardiovascular and diabetes risk. At 180 lbs, losing 9–18 lbs has documented health benefits even if BMI stays above 25. Strength training builds muscle (which improves metabolic health but may raise BMI) so track body fat % as a secondary metric. Sustainable weight loss of 0.5–1 lb/week through a 250–500 calorie daily deficit is far more effective long-term than aggressive crash dieting.
Frequently Asked Questions About BMI
What is a normal BMI?
18.5–24.9 is the WHO healthy weight range. However, Asian adults may face elevated health risks at BMI 23+, so some clinicians use 23 as a threshold for that population. For most adults, aiming for 20–23 provides good health outcomes while leaving margin above the underweight cutoff.
Why is BMI not accurate for athletes?
BMI only measures weight relative to height — it can't tell whether that weight is fat or muscle. A 5'11" linebacker at 220 lbs and 12% body fat has a BMI of 30.7 (Obese Class I), yet is metabolically healthy. For athletes, body fat percentage (measured by DEXA, calipers, or Navy method) is far more meaningful.
What is a healthy BMI for women vs. men?
The same WHO ranges apply to both sexes. However, women naturally carry 5–10% more body fat than men at the same BMI due to hormonal and reproductive differences. A woman with BMI 22 may have 25% body fat while a man with the same BMI may have 18%. Both fall within healthy ranges.
Does BMI differ by age?
For adults 20+, the same categories apply regardless of age. However, older adults (65+) with BMI 25–27 often have better health outcomes than those at 22–24, possibly because some fat reserves help survive illness. For children and teens, age- and sex-specific BMI percentiles are used instead of fixed cutoffs.
What is the average BMI in the US?
The average US adult BMI is approximately 29.0 — just below the Obese threshold. About 41.9% of US adults are obese (BMI 30+) and 30.7% are overweight (BMI 25–29.9). Only 25.6% fall in the healthy weight range. (CDC NHANES 2017–2020 data)
How do I calculate BMI manually?
Imperial: BMI = (weight in lbs × 703) / (height in inches)². Metric: BMI = weight (kg) / height (m)². Example: 160 lbs, 5'6" = (160 × 703) / (66)² = 112,480 / 4,356 = 25.8 BMI.
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