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BMI Calculator

Body Mass Index (BMI) is a standardized screening metric that evaluates the mathematical relationship between an individual's weight and height. First

Health & Fitness
Select preferred unit system for body measurements
Standing height (cm for metric, inches for imperial)
Current body weight (kg for metric, lb for imperial)
Adults ≥ 20 use fixed cutoffs; youth < 20 require pediatric growth percentiles
Select reference population criteria for screening category cutoffs
Formula & Methodology
Metric: BMI = weight (kg) ÷ [height (m)]² | Imperial: BMI = 703 × weight (lb) ÷ [height (in)]²

In the metric system, BMI equals weight in kilograms divided by height in metres squared. In the imperial system, weight in pounds is divided by height in inches squared and multiplied by the conversion factor 703 (a rounded approximation of 703.0695796 derived from 0.45359237 kg/lb ÷ [0.0254 m/in]²). Healthy weight ranges correspond to the BMI interval 18.5 to 24.9 kg/m².

Body Mass Index — Normal weight

22.9 kg/m²

Overview

Body Mass Index (BMI) is a standardized screening metric that evaluates the mathematical relationship between an individual's weight and height. First formulated by Belgian polymath Adolphe Quetelet in the 19th century, BMI provides public health researchers and clinicians with a fast, non-invasive population screening index.

Educational & Safety Disclaimer: This calculator provides generalized estimates based on published World Health Organization equations. It is not medical advice, does not provide clinical diagnosis or treatment, and does not evaluate personal health status. Consult a qualified physician or healthcare provider for personal health evaluations.

Worked Examples

Metric Adult Example: 70 kg and 1.75 m

Height = 175 cm (1.75 m), Weight = 70 kg, Age = 30, WHO Standard.

  1. Convert height to metres: 175 cm ÷ 100 = 1.75 m.
  2. Square height in metres: 1.75 × 1.75 = 3.0625 m².
  3. Divide weight by height squared: 70 ÷ 3.0625 = 22.8571... kg/m².
  4. Round display to one decimal place: 22.9 kg/m² (Normal weight).
Final Answer: 22.9 kg/m² (Normal weight)

Imperial Adult Example: 154.32 lb and 68.9 in

Height = 68.9 in, Weight = 154.32 lb, Imperial 703 factor.

  1. Square height in inches: 68.9 × 68.9 = 4,747.21 in².
  2. Multiply weight by 703: 154.32 × 703 = 108,486.96.
  3. Divide product by height squared: 108,486.96 ÷ 4,747.21 = 22.8527... kg/m².
  4. Round display to one decimal place: 22.9 kg/m² (Agrees with metric within 0.1).
Final Answer: 22.9 kg/m² (Normal weight)

Asian Population Cutoff Comparison: BMI 24.0 at 170 cm

Height = 170 cm (1.70 m), Weight = 69.36 kg (BMI = 24.0).

  1. Height squared: 1.70 × 1.70 = 2.89 m².
  2. BMI: 69.36 ÷ 2.89 = 24.0 kg/m².
  3. Under WHO International Standard: 24.0 falls in Normal weight (18.5 – 24.9).
  4. Under WHO Asian Population Criteria: 24.0 falls in Overweight / Increased Risk (23.0 – 27.4).
Final Answer: 24.0 kg/m² (Overweight / Increased Risk under Asian criteria)

How to Use This Calculator

  1. Select your preferred measurement system (Metric cm/kg or Imperial in/lb).
  2. Enter your exact standing height and current body weight without footwear.
  3. Enter your age and select whether to view standard international or Asian population cutoffs.
  4. Review your calculated BMI, population classification band, and reference healthy weight range.

Frequently Asked Questions

Is BMI an accurate measure of body fat for athletic individuals?
No. BMI evaluates total body mass relative to stature and cannot differentiate between skeletal muscle mass, adipose tissue, bone density, or bodily fluids. Highly trained individuals and strength athletes frequently classify as overweight or obese on BMI scales while maintaining low body fat percentages.
Why do Asian populations have different BMI cutoff thresholds?
World Health Organization epidemiological studies demonstrated that individuals of Asian ancestry typically possess a higher proportion of body fat and higher prevalence of cardiovascular and type 2 diabetes risk at lower BMI values than European populations. Consequently, WHO established revised screening cutoffs (overweight at 23.0 kg/m² and obesity at 27.5 kg/m²).
Why does this calculator require a growth chart for children and teens under 20?
Body composition fluctuates dramatically throughout childhood and adolescence due to growth spurts and sexual maturation. Fixed adult BMI thresholds are clinically invalid for under-20s; instead, BMI percentiles compared against age-and-sex-specific CDC or WHO growth charts are required.
How is the imperial 703 conversion factor derived?
The factor 703 originates from converting metric units: (1 lb = 0.45359237 kg) divided by (1 in = 0.0254 m)² = 0.45359237 ÷ 0.00064516 ≈ 703.06958. Standard imperial equations round this constant to 703, producing fractional differences in the second or third decimal place.
Does a normal BMI guarantee optimal metabolic health?
No. A normal BMI does not preclude normal-weight obesity (high visceral body fat with low muscle mass), elevated blood lipids, hypertension, or insulin resistance. BMI is a preliminary statistical screening tool rather than a comprehensive diagnostic assessment.

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Reviewed & Authored by: OnlineConvers Health & Quantitative Science Editorial Team · Last Updated: 2026-10-07
Calculates Body Mass Index using the standard Quetelet equation: BMI = mass (kg) ÷ height (m)². Imperial inputs are evaluated using the published constant 703 × weight (lb) ÷ height (in)². Classification categories are established on unrounded values using either WHO International Standards (Normal: 18.5–24.9, Overweight: 25.0–29.9, Obese: ≥30.0) or WHO Asian Population Cutoffs (Normal: 18.5–22.9, Overweight: 23.0–27.4, Obese: ≥27.5). Conversions use exact international standards: 1 lb = 0.45359237 kg and 1 in = 0.0254 m.
Citations: Physical status: The use and interpretation of anthropometry (World Health Organization Technical Report Series 854 (1995)) · Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies (The Lancet (WHO Expert Consultation, 2004)) · Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults (National Institutes of Health / NHLBI (1998))