How do I calculate my BMI?

Enter your height and weight into the calculator. BMI is calculated as weight (kg) divided by height squared (m²). For imperial units, the formula is (weight in lbs ÷ height² in inches) × 703. Our calculator handles the math automatically.

What is a healthy BMI range?

A healthy BMI is between 18.5 and 24.9. Below 18.5 is underweight, 25-29.9 is overweight, and 30+ is obese. However, BMI is just one indicator — muscle mass, age, and other factors also matter.

Is BMI different for men and women?

The BMI formula is the same for men and women. However, women typically have more body fat than men at the same BMI. The calculator shows healthy ranges that apply to both genders, though individual assessments may vary.

Does age affect BMI interpretation?

For adults, standard BMI categories apply regardless of age. For children and teens (2-19 years), BMI is interpreted using age- and sex-specific percentiles. Older adults may have slightly different healthy ranges.

What BMI should I have for my height?

For a healthy BMI (18.5-24.9), your ideal weight depends on your height. The calculator shows your healthy weight range based on your height. For example, someone 170 cm tall should weigh between 53-72 kg.

How accurate is BMI as a health indicator?

BMI is a useful screening tool but has limitations. It doesn't account for muscle mass, bone density, or fat distribution. Athletes may have high BMI due to muscle. For a complete assessment, consider waist circumference, body fat percentage, and other metrics.

Can I use BMI for weight loss goals?

Yes! The calculator shows your healthy weight range based on BMI. If your current weight is above this range, you can set a target weight within the healthy BMI zone. Aim for gradual weight loss of 0.5-1 kg per week.

What's the difference between BMI and body fat percentage?

BMI estimates body fat based on height and weight only. Body fat percentage measures actual fat mass. BMI can misclassify muscular people as overweight. For precise body composition, consider DEXA scans or skinfold measurements.

How do I convert between metric and imperial for BMI?

Our calculator supports both systems. For metric: use kg and cm. For imperial: use lbs and inches. The BMI result is the same regardless of which system you use — just select your preferred unit system.

How is BMI calculated for children and teens?

For ages 2–19, BMI is interpreted using age- and sex-specific CDC percentiles, not fixed numbers. Under 5th percentile is underweight; 5–84th is healthy weight; 85–94th is overweight; 95th+ is obese. A child's BMI number doesn't classify them directly — it's compared to peers of the same age and sex. Use our calculator to get the BMI number, then interpret it via the CDC BMI Percentile Calculator for children. Always consult a pediatrician for medical interpretation.

Which groups should not rely on BMI alone?

Competitive athletes and bodybuilders (muscle mass inflates BMI), adults over 65 (muscle loss masks elevated body fat), pregnant and breastfeeding women (use pre-pregnancy BMI), people with amputations, and those at extreme height (below 5'0 or above 6'4). If any apply to you, pair BMI with waist circumference, body-fat percentage, and clinical guidance.

Does BMI change during menopause?

BMI calculation doesn't change — same formula — but many women gain 5–10 lbs (2–5 kg) during and after menopause due to hormonal shifts and muscle loss, pushing their BMI up without lifestyle changes. Waist circumference often captures menopausal metabolic risk more accurately. Work with your clinician to set a personalized target, especially if you have a history of cardiovascular disease or diabetes.

What is a healthy BMI after pregnancy?

Do not use BMI as a benchmark immediately postpartum. Allow 6–12 months for body composition to normalize. Pre-pregnancy BMI is the correct reference for tracking weight gain during pregnancy (via Institute of Medicine / NHS guidance) and for setting postpartum goals. Consult your healthcare provider before starting weight-loss efforts, especially if breastfeeding.

What is waist-to-height ratio (WHtR) and should I use it?

WHtR = waist circumference ÷ height (same units). Under 0.5 is healthy — the 'keep your waist less than half your height' rule. WHtR measures abdominal fat, which drives cardiovascular and metabolic disease better than BMI can. NHS (UK) updated its guidelines in 2023 to recommend WHtR alongside BMI. Use both: a normal BMI with WHtR above 0.5 still signals elevated risk (skinny fat); a high BMI with WHtR below 0.5 usually means muscle.

BMI Prime is your BMI divided by 25 (the overweight threshold). A value of 1.0 means you're at the overweight borderline; 0.8 is bottom of healthy range; 1.2 means you're 20% above the overweight cutoff. It's a quick way to see how far above or below the healthy-weight ceiling you are.

What is the Ponderal Index?

Ponderal Index (weight ÷ height³) is a BMI alternative that accounts better for height. Especially useful for very tall or very short adults whom BMI can misclassify. A healthy Ponderal Index is roughly 11–15 kg/m³. It remains informational only — BMI is still the primary screening tool used by CDC, NHS, Health Canada and Heart Foundation Australia.

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BMI Calculator

calculators.im ↗

Unit System

Height

Weight

lbs

Your BMI

24.2

Normal Weight

BMI Scale

16 18.5 25 30 35 40+

Underweight Normal Overweight Obese

Healthy Weight Range

Min

53.5 kg

Max

72.3 kg

You're at a healthy weight!

Input Values

Unit System

Imperial (lb/in)

Metric (kg/cm)

lightbulb Tips

•Healthy BMI: 18.5-24.9
•BMI doesn't measure body fat directly
•Athletes may have high BMI from muscle
•Consult doctor for complete assessment

monitoring BMI Categories

Severe Underweight < 16

Underweight 16 - 18.4

Normal Weight 18.5 - 24.9

Overweight 25 - 29.9

Obese Class I 30 - 34.9

Obese Class II 35 - 39.9

Obese Class III ≥ 40