BMI Calculator

BMI Calculator

Calculate your Body Mass Index (BMI) weight classification index instantly using local browser memory.

Input Methodology

1. 1Select Unit System: Choose Metric (kg/cm) or Imperial (lbs/inches).
2. 2Enter Weight: Input your body weight in the selected unit.
3. 3Enter Height: Input your height in the selected unit.
4. 4Review Results: See your BMI value and its corresponding WHO classification.

BMI Calculator — Body Mass Index for Adults

If you weigh 75 kg and are 1.8 meters tall, your Body Mass Index (BMI) is calculated as 75 / (1.8)², resulting in a value of 23.15, placing you in the 'Normal weight' category. While BMI is a quick screening tool, it does not distinguish muscle mass from fat—a bodybuilder could be classified as 'Obese' due to muscle weight alone. This tool provides your baseline classification.

• BMI Shows a Very Low Number (e.g. 0.27): You likely entered height in centimetres when the metric formula expects metres. Convert: 175 cm = 1.75 m.
• BMI Seems Unchanged Despite Weight Loss: A 1 kg loss at 178 cm changes BMI by only ~0.3 points. Check your input precision.
• Imperial Results Differ From Other Tools: Confirm you are using total inches for height (5'9" = 69 inches, not 5.9).

Does BMI measure body fat percentage?

No. BMI is derived only from weight and height. It cannot distinguish fat from muscle, bone density, or water. Body fat percentage requires methods like DEXA scanning, skinfold calipers, or bioelectrical impedance.

Why is the adult BMI formula not used for children?

Children's bodies change proportionally as they grow. A fixed BMI cut-off would misclassify normal development stages as underweight or overweight. Paediatric assessment uses BMI-for-age percentile charts adjusted for sex and age.

Does the same BMI threshold apply across all ethnic groups?

No. Research shows that populations of Asian descent face higher cardiometabolic risk at lower BMI values. The WHO has proposed lower thresholds (23 for overweight, 27.5 for obese) for Asian populations.

Is my health data stored anywhere?

No. All calculations run client-side in your local browser. Your inputs are never uploaded.

• Calorie Calculator: Determine daily calorie targets for weight maintenance, loss, or gain.
• BMR Calculator: Determine your Basal Metabolic Rate (BMR) using Mifflin-St Jeor formula.
• Water Intake Calculator: Calculate standard daily hydration requirements relative to weight and exercise load.
• Ideal Weight Calculator: Determine estimated ideal body weights based on Devine and Robinson equations.
• Body Fat Calculator: Estimate body fat percentage using US Navy circumference methodologies.
• Protein Intake Calculator: Calculate standard daily protein guidelines for body composition goals.

Mathematical Formula & Standards

The underlying calculations for the BMI Calculator follow the standard formula: Metric: weight (kg) / height (m)^2 | Imperial: (weight (lbs) / height (in)^2) * 703.

Result Interpretation Guidance

• Office Worker (Metric): Weight 82 kg, Height 178 cm. BMI = 82 / (1.78)² = 25.9. Category: Overweight. This result flags a need to reduce caloric surplus, not an emergency health risk.
• Athlete (Imperial): Weight 200 lbs, Height 70 inches. BMI = (200 / 4900) × 703 = 28.7. Category: Overweight — but if this individual has 12% body fat, BMI significantly overstates their health risk.

• Adults Tracking Weight Changes: Monitoring BMI trends over time as one indicator of weight-related health risk.
• Fitness Enthusiasts: Setting a baseline before starting a structured training or nutrition program.
• Parents of Adolescents: Note that this tool uses the adult BMI formula — a different age-adjusted percentile method applies to children under 18.
• Healthcare Screening: Quickly screening adults in community health settings where formal clinical tools are unavailable.

• As a first-step health screening tool when beginning a weight management program.
• Tracking directional weight progress over weeks or months (not day-to-day, which is dominated by hydration and meal timing noise).
• When a healthcare provider asks you to report your BMI for pre-consultation intake forms.

• Athletes and Bodybuilders: BMI does not distinguish between muscle mass and fat mass. A 90 kg athlete at 175 cm has a BMI of 29.4 (overweight category) despite having low body fat — because the formula only knows weight and height.
• Children Under 18: Adult BMI cut-offs do not apply to children. Use age-adjusted BMI-for-age percentile charts from the CDC or WHO.
• Pregnant Women: Weight changes during pregnancy make BMI an unreliable indicator of pre-pregnancy body composition.
• Older Adults (65+): Research suggests that slightly higher BMI values (25–27) may actually be associated with better survival outcomes in older populations.

BMI is a simple weight-to-height ratio, not a direct measure of body fat:

1. 1Metric Formula:

BMI = (Weight (kg) / Height (m)^2)

1. 2Imperial Formula:

BMI = (Weight (lbs) / Height (inches)^2) * 703

1. 3WHO Classification Tiers:

[Weight & Height (Metric or Imperial)]
              |
              v
[BMI = Weight / Height²  (with 703 conversion for imperial)]
              |
              v
[BMI Value + WHO Category + Risk Tier Label]

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