BMI Calculator

Calculate your body mass index (weight in kg divided by height in metres squared) and see your WHO weight category, with notes on where BMI misleads.

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Estimated body fat percentage: %

Interpretation:
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    Standard BMI Categories (WHO / CDC for adults):
    • Underweight: < 18.5
    • Normal weight: 18.5 – 24.9
    • Overweight: 25.0 – 29.9
    • Obesity class I: 30.0 – 34.9
    • Obesity class II: 35.0 – 39.9
    • Obesity class III: ≥ 40.0
    BMI is a screening tool only. It does not diagnose health. Estimated body fat % uses Deurenberg formula (BF% = 1.20 × BMI + 0.23 × Age − 10.8 × Sex − 5.4), where Sex = 1 for male, 0 for female. This is an approximation (SEE ≈ 4.1%). BMI does not account for muscle mass, ethnicity, pregnancy, etc. Consult a doctor for health assessment.

    Important note: This calculator provides general estimates only. For accurate health assessment, please consult a qualified healthcare professional.

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    Calculation Examples

    Calculation Case Result
    Height 175 cm, weight 70 kg BMI 22.9, normal weight
    Height 180 cm, weight 95 kg BMI 29.3, overweight (14.3 kg above the 24.9 limit)
    Height 160 cm, weight 45 kg BMI 17.6, underweight (WHO mild thinness, 17.0 to 18.49)
    Height 170 cm, weight 90 kg (athlete) BMI 31.1, obese class I. May overestimate risk in high-muscle people, so check waist and body fat
    Mihail Doncenco
    Mihail Doncenco Site Creator & Calculator Expert

    Founder and developer of CalcMate. Builds and maintains every calculator on this site, focusing on formula accuracy and clear, practical results.

    How to Use the BMI Calculator

    Enter your height and weight, choose your units (metric: kg and cm; imperial: lb and inches) and click "Calculate". The calculator applies the formula \[ \text{BMI} = \frac{\text{weight (kg)}}{\text{height (m)}^2} \] and shows your value with the matching WHO category for adults: underweight (below 18.5), normal weight (18.5 to 24.9), overweight (25.0 to 29.9) or obese (30.0 and above). In imperial units the equivalent formula is \(\text{BMI} = 703 \times \text{weight (lb)} \div \text{height (in)}^2\).

    BMI is a screening tool, not a diagnosis. It is quick and cheap, and WHO uses it to monitor weight at population level, but clinicians pair it with waist circumference and medical history. For a 175 cm adult, the normal range of 18.5 to 24.9 covers 56.7 to 76.3 kg. These are estimates for healthy adults, not medical advice.

    Obesity reasons and prevention

    Limitations of BMI

    BMI is derived from height and weight only, so it does not measure body fat or show where fat sits. It cannot separate fat from lean mass: a muscular athlete who is 180 cm and 87.5 kg has a BMI of 27 and lands in the "overweight" category with low body fat, while an older adult with age-related muscle loss (sarcopenia, as defined by the European Working Group on Sarcopenia in Older People) can have a "normal" BMI of 22 and a high share of body fat. In 2025, a Lancet Diabetes & Endocrinology Commission on clinical obesity concluded that BMI alone should not be used to diagnose obesity, and recommended confirming it with waist circumference or another body-size measure, or with a direct body fat measurement.

    The adult thresholds do not apply to children and adolescents, who need age- and sex-specific BMI-for-age percentiles, or to pregnant women. For Asian populations, a WHO Expert Consultation (Lancet, 2004;363:157-163) found that type 2 diabetes and cardiovascular risk rise at lower BMI values, and proposed public health action points at 23.0 (increased risk) and 27.5 (high risk). It did not replace the international classification, and national cut-offs differ: China uses 24 for overweight and 28 for obesity, Japan and South Korea use 25 for obesity, and South Korea also uses 23 for overweight. Read BMI together with waist circumference and, where available, body fat percentage.

    BMI classification chart: underweight, normal, overweight and obese thresholds

    Useful Tips 💡

    • Measure weight and height under the same conditions each time, ideally in the morning before eating, without shoes and in light clothing.
    • Record your measurements in one unit system (metric or imperial) so comparisons stay valid.
    • BMI moves slowly: 1 kg changes it by only about 0.33 for a 175 cm adult. Check it every 3 to 6 months, and use calorie intake, activity and sleep for week-to-week monitoring.

    📋Steps to Calculate

    1. Enter your weight and height in the fields provided.

    2. Select your preferred unit system: metric (kg/cm) or imperial (lb/inches).

    3. Click "Calculate" to view your BMI value and WHO weight category.

    Mistakes to Avoid ⚠️

    1. Mixing unit systems. Entering 70 kg while the pounds option is selected is read as 70 lb (31.8 kg) and gives a BMI of 10.4 instead of 22.9.
    2. Using BMI as the only health metric for athletes or strength trainers, whose muscle mass the formula cannot separate from fat mass.
    3. Applying the adult calculator to children under 18, who need BMI-for-age percentile charts, or to pregnant women, whose normal weight gain distorts the reading.
    4. Ignoring waist circumference. Two people with the same BMI can carry very different amounts of visceral fat, and waist size shows that difference.

    Practical Applications📊

    1. Track your weight category every 3 to 6 months, which gives useful trend data without over-measuring. For a 180 cm adult at 95 kg (BMI 29.3), reaching the top of the normal range (24.9) means about 80.7 kg, a loss of 14.3 kg.

    2. Use BMI with our Calorie Calculator (TDEE) to set a calorie target. A 500 kcal/day deficit starts at about 0.45 kg of loss per week, so 14.3 kg takes roughly 7 to 8 months, and longer as loss slows.

    3. If you are near a category boundary or have a lot of muscle, cross-check with our Body Fat Calculator (US Navy Method) and your waist circumference. NHLBI guidelines flag a waist above 102 cm in men and 88 cm in women as higher risk.

    Questions and Answers

    Do BMI thresholds differ for Asian populations?

    Yes, risk starts at lower BMI values in Asian populations, and WHO proposed action points for them. A WHO Expert Consultation (Lancet, Vol. 363, Issue 9403, January 2004) found higher type 2 diabetes and cardiovascular risk at lower BMI, and proposed action points at \(\text{BMI} \geq 23.0\) for increased risk and \(\text{BMI} \geq 27.5\) for high risk, against the international 25.0 and 30.0. It kept the international classification, and national cut-offs differ: China uses 24 and 28, Japan and South Korea use 25 for obesity, and South Korea also uses 23 for overweight. Part of the reason is that Asian adults tend to carry more visceral fat at the same BMI than European adults.

    How often should I track my BMI for effective health monitoring?

    Checking BMI every 3 to 6 months is enough to monitor long-term weight trends. BMI responds slowly: 1 kg changes it by only about 0.33 for a 175 cm adult, so it cannot show week-to-week changes. For active management, track calorie balance against TDEE (total daily energy expenditure), protein and other macronutrients, and NEAT (non-exercise activity thermogenesis, the calories burned through everyday movement). Use BMI as a periodic checkpoint that places those short-term metrics within your longer-term weight trend.

    What are the primary limitations of using BMI as a health metric?

    BMI cannot tell fat mass from muscle or bone, so it can overstate risk in muscular people and understate it in older adults with sarcopenia (a term Rosenberg coined in 1989 for age-related muscle loss). A muscular athlete at BMI 28 is not overweight in the clinical sense, while an older adult at a normal BMI can carry a high share of visceral fat. In 2025, a Lancet Diabetes & Endocrinology Commission advised against diagnosing obesity from BMI alone. Pair BMI with waist circumference (NHLBI guidelines flag above 102 cm in men and 88 cm in women) and body fat percentage, for example from the US Navy method, which is commonly cited at about ±3 percentage points.

    What are the WHO BMI classification thresholds for adults?

    For adults aged 20 and older, WHO defines underweight as \(\text{BMI} < 18.5\), normal weight as \(18.5 \leq \text{BMI} < 25.0\), overweight as \(25.0 \leq \text{BMI} < 30.0\) and obesity as \(\text{BMI} \geq 30.0\). Obesity is split into class I (30.0 to 34.9), class II (35.0 to 39.9) and class III (40.0 and above). Underweight is graded too: below 16.0 is severe thinness, 16.0 to 16.99 moderate and 17.0 to 18.49 mild. The thresholds are the same for men and women, but at the same BMI women usually carry a higher fat percentage than men, and athletes can fall in the overweight range with low body fat.

    What is a BMI calculator and how does it work?

    A BMI calculator divides your weight in kilograms by your height in metres squared and maps the result to a WHO weight category: \[ \text{BMI} = \frac{\text{weight (kg)}}{\text{height (m)}^2} \] Adolphe Quetelet developed the index in the 1830s, and Ancel Keys named it body mass index in 1972. For a person who is 175 cm and 70 kg: \(\text{BMI} = 70 / 1.75^2 = 70 / 3.0625 \approx 22.9\), which is normal weight. BMI does not measure body fat directly, so treat it as a screening indicator and not a diagnosis.

    Why is BMI-for-age percentile used for children and teenagers?

    Children and teenagers need BMI-for-age percentiles because body fat changes a lot during normal growth, so fixed adult cut-offs do not fit. The CDC compares a child BMI with a reference population of the same age and sex (ages 2 to 19): underweight is below the 5th percentile, healthy weight from the 5th to below the 85th, overweight from the 85th to below the 95th and obesity at or above the 95th. The WHO growth reference for ages 5 to 19 uses standard deviations instead, with overweight above +1 SD and obesity above +2 SD. These charts account for growth spurts and puberty.
    Disclaimer: This calculator is designed to provide helpful estimates for informational purposes. While we strive for accuracy, financial (or medical) results can vary based on local laws and individual circumstances. We recommend consulting with a professional advisor for critical decisions.