BMI Calculator
Enter your height and weight to calculate your BMI, see your WHO classification, find your healthy weight range, and understand what the number actually means for your health.
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Enter your values above to see the results.
Tips & Notes
- ✓Weigh yourself in the morning, before eating, after using the bathroom, and without shoes or heavy clothing — this gives the most consistent baseline reading.
- ✓BMI does not measure body fat directly. A person with 90 kg of muscle and 10 kg of fat has the same BMI as someone with 50 kg of muscle and 50 kg of fat at the same height.
- ✓For adults over 65, research suggests BMI 25–27 may be associated with better outcomes than the standard "normal" range of 18.5–24.9 — discuss with your doctor before targeting the lower range.
- ✓Asian populations face increased cardiometabolic risk at BMI 23–24, which falls within the standard "normal" range. Many Asian health authorities use BMI ≥ 23 as the overweight threshold.
- ✓Track BMI trends over months, not days. Daily weight fluctuations of 1–2 kg from water, food, and hormonal changes are normal and should not drive health decisions.
Common Mistakes
- ✗Treating BMI as a diagnostic result rather than a screening indicator — it flags who might need further assessment, not who has a disease.
- ✗Using adult BMI categories for children and teenagers, who require age- and sex-specific growth chart percentiles instead.
- ✗Measuring height with shoes on or weight fully clothed, which can inflate BMI by half a point or more.
- ✗Applying a single BMI reading to make major dietary or medical decisions without considering muscle mass, body fat distribution, or metabolic health markers.
- ✗Ignoring waist circumference, which captures visceral fat risk that BMI completely misses — two people with identical BMI can have very different cardiovascular risk profiles.
BMI Calculator Overview
BMI is the standard opening question in almost every weight-related medical conversation — and for good reason. It is fast, free, and reasonably predictive of metabolic risk at the population level. Knowing your number lets you enter that conversation informed.
BMI formula — metric and imperial:
BMI = weight (kg) ÷ height (m)² Imperial shortcut: BMI = 703 × weight (lb) ÷ height (in)²
EX: Person weighs 80 kg, stands 175 cm (1.75 m) BMI = 80 ÷ (1.75)² = 80 ÷ 3.0625 = 26.1 → Overweight category Healthy weight range for 175 cm: 56.7 – 76.3 kg (BMI 18.5 – 24.9)
Calculating your target weight from a goal BMI:
To find the weight you need to reach a target BMI: Target weight (kg) = target BMI × height (m)²
EX: Same person (175 cm) wants BMI = 24.0 Target weight = 24.0 × (1.75)² = 24.0 × 3.0625 = 73.5 kg They need to lose approximately 6.5 kg to reach that target.
WHO BMI classification — complete reference:
| BMI Range | WHO Category | Associated Risk |
|---|---|---|
| Below 16.0 | Severe Thinness | Very high (malnutrition, organ damage) |
| 16.0 – 16.9 | Moderate Thinness | High |
| 17.0 – 18.4 | Mild Thinness | Moderate |
| 18.5 – 24.9 | Normal Weight | Low (reference range) |
| 25.0 – 29.9 | Overweight | Increased |
| 30.0 – 34.9 | Obesity Class I | High |
| 35.0 – 39.9 | Obesity Class II | Very high |
| 40.0 and above | Obesity Class III | Extremely high |
BMI thresholds by population group:
| Population | Overweight threshold | Obesity threshold | Why it differs |
|---|---|---|---|
| WHO (global standard) | BMI ≥ 25 | BMI ≥ 30 | Baseline reference |
| Asian populations | BMI ≥ 23 | BMI ≥ 27.5 | Higher metabolic risk at lower BMI |
| Adults over 65 | BMI ≥ 25 (same) | BMI ≥ 30 (same) | BMI 25–27 may be protective in elderly |
| Children (2–19) | 85th–94th percentile | 95th percentile+ | Age- and sex-specific charts, not adult cutoffs |
BMI has a well-documented blind spot: it cannot distinguish fat from muscle. A professional rugby player at 1.80 m and 100 kg has a BMI of 30.9 — "Obese Class I" — yet may carry less than 12% body fat. Conversely, a sedentary person with a BMI of 23 might have 30% body fat — "normal weight obesity" — with the same cardiovascular risk as someone classified as overweight. Waist circumference (above 94 cm for men, 80 cm for women) is the fastest supplementary check. If your BMI is borderline and your waist is within range, your risk profile looks quite different than the number alone suggests.
Frequently Asked Questions
The standard healthy BMI range (18.5–24.9) applies to adults of all ages, but interpretation shifts with age. For adults over 65, research suggests that BMI 25–27 may be associated with lower mortality than the standard normal range, possibly because some extra weight provides a reserve during illness. For adults under 65, staying within 18.5–24.9 is the general target, though muscle mass matters — a fit 40-year-old with BMI 26 and 15% body fat has a very different risk profile than a sedentary person at the same BMI with 30% body fat.
The BMI formula is identical for men and women, but the health implications at the same BMI differ. Women naturally carry 5–10% more body fat than men at the same BMI due to biological differences in hormones and fat distribution. This means a woman at BMI 23 typically has higher body fat percentage than a man at BMI 23, yet this is normal and expected. The standard BMI categories apply to both sexes, but some researchers argue women's thresholds should be slightly different to account for these differences.
Yes. BMI below 18.5 is classified as underweight and is associated with risks including reduced bone density, immune suppression, nutritional deficiencies, anemia, and in severe cases, cardiac complications. Some people naturally have low BMI due to genetics, high activity, or small frame without any health problems. However, if you have reached a low BMI through restrictive eating or significant unintentional weight loss, medical evaluation is warranted regardless of how you feel subjectively.
Muscle weighs more per unit volume than fat. Regular resistance training builds lean mass, which raises body weight and therefore BMI without increasing fat. A 175 cm person with BMI 27 who has 15% body fat and visible muscle definition is in a completely different health category than someone with the same BMI and 30% body fat. If you exercise regularly and suspect muscle is inflating your BMI, a body fat percentage assessment (Navy method, skinfold calipers, or DEXA) gives a more meaningful picture of your composition.
BMI is calculated from height and weight alone — it has no information about what your weight is made of. Body fat percentage measures the proportion of your total weight that is actually fat tissue, distinguishing it from muscle, bone, water, and organs. Two people can have identical BMIs but dramatically different body fat percentages depending on their muscle mass. Body fat percentage is a more direct measure of composition but requires additional measurements (circumferences, skinfolds, or imaging), which is why BMI remains the quick screening tool.
For general health monitoring, checking BMI monthly or quarterly is sufficient — daily checks add no useful information due to normal weight fluctuations. If you are actively working toward a weight goal (loss or gain), monthly checks with consistent measurement conditions (same time of day, same scale) let you track real trends without reacting to noise. Each time you calculate, note your waist circumference alongside your BMI for a more complete picture.