BMI Calculator
What BMI measures, what it misses, and the calculators to work it out properly - including the ones that answer better questions than BMI does.
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BMI Categories and Where the WHO Cut-Offs of 25 and 30 Come From
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BMI Calculator Explained: The Formula It Runs, the Categories It Reports, and the Rounding
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How to Weigh Yourself So the Number Means Something: Time, Clothing, Frequency
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BMI in Athletes and Muscular Builds: How Far It Overstates Risk, with Measured Examples
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How Child BMI Percentiles Work and What They Actually Measure
Guides by category
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BMI and health risk
BMI is associated with mortality and disease risk at the population level, but the relationship is shaped by confounding, reverse causation, and body composition differences.
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Body composition
BMI measures weight-for-height, not body composition. This hub routes you to guides on waist-to-height ratio, body fat percentage, visceral fat, and muscle mass, with every threshold attributed to its source.
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Children and teenagers
How to understand a child's BMI result, growth chart position, and what it means for health, with every threshold attributed to its issuing body and year.
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Measuring it properly
Self-reported numbers produce a BMI roughly 0.5-1.5 kg/m² lower than measured ones. These guides give you the protocol to close that gap, with the error size named for each step.
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The calculators
Route to the right body measurement calculator by what you are trying to understand, with every equation's source and margin of error stated before you enter a number.
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Understanding BMI
Understanding body mass index: a hub routing you to guides on BMI screening, measurement methods, population thresholds, and what BMI can and cannot tell you.
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Weight and energy balance
How basal metabolic rate, total daily energy expenditure, calorie deficit and metabolic adaptation interact—explained through mechanisms, not prescriptions.
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When BMI reads wrong
Which populations standard BMI misclassifies—athletes, older adults, pregnant women, and ethnic groups—and what measurements are used instead, with every threshold sourced.
Latest articles
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BMI and Mortality: The J-Shaped Curve, Confounders, and the Evidence
Observational studies show a J-shaped relationship between BMI and mortality. Reverse causation and smoking confound the low end; Mendelian randomisation suggests a more linear causal effect.
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Basal Metabolic Rate Explained: BMR Equations, Error Ranges and Accuracy
Basal metabolic rate is measured under strict conditions; prediction equations estimate it with individual error typically ±10–20%, and some groups face systematic bias.
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Waist-to-Height Ratio: The 0.5 Rule and How to Measure Your Waist
The NICE CG189 (2022) guideline advises keeping waist-to-height ratio below 0.5. Learn what this ratio predicts, how it differs from BMI, and the correct waist measurement protocol with its error margins.
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What BMI is and how it is calculated Review: Specifications, Range and Who It Suits
What What BMI is and how it is calculated claims, what owners report, and the one trade-off that decides whether it is the right machine.
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Weight and Energy Balance Explained: BMR, TDEE, Deficit and Maintenance
How basal metabolic rate, total daily energy expenditure, calorie deficit and metabolic adaptation interact—explained through mechanisms, not prescriptions.
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When BMI Reads Wrong: Populations for Whom Standard BMI Misclassifies Health Risk
Which populations standard BMI misclassifies—athletes, older adults, pregnant women, and ethnic groups—and what measurements are used instead, with every threshold sourced.
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BMI Calculator: Understand Your Body Mass Index Number and Its Limits
Use this BMI calculator to see your number and learn what the WHO categories from 1995 actually mean for one person—and what they cannot tell you about your body.
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TDEE Calculator: Estimate Your Total Daily Energy Expenditure as a Range
Estimate your total daily energy expenditure and understand why the Mifflin-St Jeor equation produces a range, not a single accurate number for any individual.
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Body Fat Calculator: US Navy Method Estimate and Its Error Against DXA
Calculate your body fat percentage using the US Navy circumference method and learn how the estimate compares to DXA, including who it reads worst for.
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Ideal Weight Calculator: See the WHO Healthy BMI Range for Your Height
See the WHO healthy BMI weight range for your height and learn where the Devine, Robinson, Miller, and Hamwi formulas came from and why they disagree.