About BMI

Limitations

BMI doesn't account for muscle mass, bone density, or fat distribution. Athletes may score 'overweight' despite low body fat.

Healthy range

A BMI between 18.5 and 24.9 is considered healthy for most adults. Individual variation applies.

Children

BMI for children and teens uses different age- and sex-specific scales. This calculator is for adults (18+).

How to Use the BMI Calculator

Enter your height — in feet/inches or centimetres.
Enter your weight — in pounds or kilograms.
Click Calculate — see your BMI score and category (underweight, normal, overweight, obese).
Read the healthy weight range — the calculator shows the weight range considered healthy for your height.
Check the BMI table — see all BMI categories with their ranges for reference.

⚠️ BMI limitations: BMI does not measure body fat directly. A muscular athlete and an overweight sedentary person of the same height and weight get identical BMI scores but have very different health profiles. BMI is a population-level screening tool, not an individual health diagnosis. Always interpret BMI alongside other health indicators.

Understanding BMI

📐 BMI Formula

BMI = weight(kg) / height(m)². Imperial: BMI = 703 × weight(lbs) / height(inches)². A 70kg person who is 1.75m tall: 70 / (1.75²) = 70 / 3.0625 = 22.9. Created by Belgian mathematician Adolphe Quetelet in the 1830s as a population statistics tool — not originally intended as an individual health metric.

📊 BMI Categories (WHO)

Underweight: < 18.5. Normal weight: 18.5–24.9. Overweight: 25.0–29.9. Obese Class I: 30.0–34.9. Obese Class II: 35.0–39.9. Obese Class III (severe): ≥ 40. These thresholds were established for populations of European descent and may not apply equally to all ethnic groups.

🌍 Ethnic Adjustments

Asian populations have higher health risks at lower BMIs than European populations — the same BMI correlates with more body fat and greater metabolic risk. Many health organisations recommend lower thresholds for Asian populations: overweight at 23 (not 25), obese at 27.5 (not 30). South Asian populations have particularly elevated cardiovascular risk at lower BMIs.

💪 The Muscle Problem

BMI cannot distinguish muscle from fat. A 6'0" professional bodybuilder at 220lbs has BMI 29.8 (overweight) despite minimal body fat. A 6'0" sedentary person at 220lbs may have BMI 29.8 but very high body fat. BMI misclassifies approximately 30% of people when compared to direct body fat measurement.

📈 BMI and Health Risk

Despite limitations, population studies consistently show BMI correlates with health outcomes at a population level. Higher BMI is associated with increased risk of type 2 diabetes, cardiovascular disease, certain cancers, sleep apnoea, joint problems, and all-cause mortality. The correlation is strong at population level even if individual BMI is imprecise.

🔄 Better Alternatives

Waist circumference: men >40 inches (102cm), women >35 inches (88cm) indicates increased risk. Waist-to-hip ratio: >0.90 for men, >0.85 for women indicates risk. Waist-to-height ratio: >0.5 indicates risk (same threshold regardless of sex). Body fat percentage (from DEXA, BodPod, or Navy formula) is most accurate but least accessible.

BMI in Health Context

BMI as a starting point, not endpoint

Use BMI as an initial screening tool, then investigate further if the result raises concerns. A BMI in the overweight range warrants checking waist circumference (better visceral fat indicator), blood pressure, fasting glucose, and lipid panel. These metabolic markers together with BMI provide a much more complete health picture than BMI alone. Many people with 'overweight' BMI have completely healthy metabolic profiles; some people with 'normal' BMI have poor metabolic health — a phenomenon called 'normal weight obesity.'

BMI in children

BMI assessment in children uses age and sex-specific percentile charts rather than fixed thresholds — because healthy BMI changes with age and differs between boys and girls during development. A BMI that is 'healthy' for a 5-year-old is 'underweight' for a 15-year-old. Paediatricians plot BMI on CDC or WHO growth charts and assess percentile rank rather than absolute BMI value. Parental BMI is also relevant context for paediatric BMI assessment.

Weight management beyond BMI

If BMI indicates overweight or obesity and metabolic markers confirm elevated risk, the evidence-based approach to weight management: sustained calorie deficit through dietary change (most impactful for weight), regular physical activity (most impactful for metabolic health independent of weight), adequate sleep (poor sleep increases appetite hormones), and stress management (chronic stress elevates cortisol, promoting fat storage). No single approach works for everyone — personalised plans with healthcare provider guidance produce the best outcomes.

📊 BMI quick reference by height: 5'4" (163cm): healthy = 108–145 lbs (49–66 kg). 5'7" (170cm): healthy = 118–159 lbs (54–72 kg). 5'10" (178cm): healthy = 129–173 lbs (59–79 kg). 6'0" (183cm): healthy = 136–183 lbs (62–83 kg). 6'2" (188cm): healthy = 144–194 lbs (65–88 kg). These ranges are BMI 18.5–24.9 converted to weight for common heights.

Frequently Asked Questions

What is BMI?

Body Mass Index = weight(kg) / height(m)². It provides a simple numerical weight classification. Underweight: <18.5. Normal: 18.5–24.9. Overweight: 25–29.9. Obese: 30+.

Why isn't BMI always accurate?

BMI doesn't distinguish muscle from fat. A muscular athlete may score 'overweight' despite very low body fat. It also ignores fat distribution, bone density, age, and sex differences.

Is BMI the same for children?

No. Children's BMI uses age- and sex-specific percentile charts. This calculator is for adults (18+). For children, consult a paediatrician or use a CDC/WHO paediatric tool.