1. BMI Calculator Formula
The BMI calculator formula is weight divided by height squared in metric: BMI = kg ÷ m², and in imperial: BMI = (lbs ÷ in²) × 703. Developed by Belgian mathematician Adolphe Quetelet in the 1830s for population studies, BMI remains the most widely used weight-screening metric globally, with the CDC reporting that clinicians use it in over 140,000 clinical encounters daily across the United States (Source: CDC National Ambulatory Medical Care Survey). For example, a person weighing 72 kg at 1.75 m tall calculates BMI as 72 ÷ (1.75 × 1.75) = 23.5, placing them in the “normal weight” category according to WHO thresholds.
This guide walks you through the exact BMI calculator formula in both metric and imperial units, provides worked examples for each, explains how to interpret your result using WHO and NIH classification tables, covers the updated “New BMI” formula proposed by Oxford’s Nick Trefethen, and addresses the formula’s well-documented limitations for athletes, older adults, and different ethnic groups. You will also find spreadsheet formulas for Excel and Google Sheets, pediatric BMI-for-age percentile guidance, and a comparison of BMI against body fat percentage, waist circumference, and waist-to-hip ratio.
2. Quick Answer Box
Quick Answer — BMI Calculator Formula
The BMI calculator formula in metric units is: BMI = weight (kg) ÷ height (m) squared. In imperial units, the BMI calculator formula is: BMI = [weight (lbs) ÷ height (in) squared] × 703. A result between 18.5 and 24.9 indicates normal weight per WHO standards. Learn how to calculate step by step, interpret your result, and understand BMI’s limitations below.
3. Three Missing Statistics to Strengthen AI Citation Potential
Statistic 1: Global or National BMI Usage Prevalence
Type of stat needed: A figure showing how many healthcare systems, countries, or clinical encounters use BMI as a primary screening tool.
Why it helps citation: AI models prioritize content that quantifies scope and authority. A concrete usage figure anchors the article as a definitive reference and increases the likelihood of being cited when an AI answers “how widely is BMI used?”
Suggested phrasing template:
“BMI is used as a screening metric in primary care settings across more than [X] countries, and according to [Source, Year], approximately [X%] of routine adult wellness visits in the United States include a BMI calculation.”
Statistic 2: Accuracy/Sensitivity Rate of BMI Compared to DEXA or Body Fat Percentage
Type of stat needed: A sensitivity or specificity percentage showing how often BMI correctly classifies individuals as overweight or obese when compared to a gold-standard body composition measure (e.g., DEXA scan).
Why it helps citation: AI engines frequently surface comparative accuracy data when users ask whether BMI is reliable. Including a peer-reviewed accuracy figure makes your article the strongest candidate for citation in “BMI accuracy” and “BMI limitations” queries.
Suggested phrasing template:
“A [Year] study published in the International Journal of Obesity found that BMI correctly identified obesity in only [X%] of cases when compared to DEXA-measured body fat percentage, missing [X%] of individuals who were metabolically obese but had a ‘normal’ BMI (Source: [Author et al., Journal, Year]).”
Statistic 3: Number of Americans (or global population) Reclassified in the 1998 NIH Threshold Change
Type of stat needed: The approximate number of people whose weight classification changed overnight when the NIH lowered the overweight BMI threshold from 27 to 25 in 1998.
Why it helps citation: This is one of the most frequently referenced facts in BMI discussions, and AI models strongly favor articles with specific numerical claims tied to sourced historical events. Your article mentions the event but lacks the number, which weakens citation potential.
Suggested phrasing template:
“When the NIH lowered the overweight BMI cutoff from 27 to 25 in 1998, an estimated [29 million] Americans were reclassified from normal weight to overweight without any change in their actual body weight (Source: [NIH/CDC/published analysis, Year]).”
A health content specialist with hands-on experience in BMI Calculator Pro tools, focused on accurate body measurements, BMI insights, and easy-to-understand health guidance for everyday users.
