BODY COMPOSITION
BMI Calculator
BMI calculator: calculate body mass index quickly and interpret the result with a body-neutral range context.
Result
BMI Position
Your BMI placed against the standard adult BMI categories.
How to use it
- Enter height and weight accurately — BMI is highly sensitive to height input. A 1-inch error changes BMI by roughly 0.6 points at average height.
- Read your BMI and category: Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese 30+. These thresholds were designed for population-level statistics and carry a ±5 point individual error margin.
- If you resistance train regularly, your BMI likely overestimates body fat. A 200 lb person at 10% body fat and 28% body fat have identical BMIs. Use the Body Fat Percentage Calculator for a better assessment.
- Add waist circumference for clinical context: cardiovascular risk rises above 35 inches (women) and 40 inches (men) regardless of BMI category.
- Use BMI to track directional trends over time, not as a precise health measurement. A BMI moving from 29 to 26 over 12 months is meaningful progress even if 26 is still above normal range.
Questions people usually ask
Is BMI accurate for muscular people?
No. BMI cannot distinguish muscle from fat. A 200 lb athlete at 10% body fat and a 200 lb sedentary person at 28% body fat have identical BMIs. Studies show BMI misclassifies about 30% of people — labeling lean-muscular individuals as overweight and some metabolically unhealthy individuals as normal.
What are the BMI ranges and what do they mean?
Underweight: below 18.5. Normal: 18.5-24.9. Overweight: 25-29.9. Obese Class I: 30-34.9. Class II: 35-39.9. Class III: 40+. These thresholds were set for population-level statistics and carry a ±5 point margin of error for individual health assessment.
Is a BMI of 25-27 actually unhealthy?
Not necessarily. Research shows all-cause mortality risk is lowest around BMI 22-25, but the overweight range (25-29.9) shows minimal elevated risk in most studies. Metabolic markers (blood pressure, fasting glucose, triglycerides) are far better individual health indicators than BMI alone.
How does BMI differ for different ethnicities?
WHO and many health authorities use lower thresholds for Asian populations: overweight begins at BMI 23, obesity at 27.5. Asian adults show increased metabolic risk at lower BMI values compared to European populations, likely due to different fat distribution patterns.
What should I use instead of BMI?
Waist circumference is a stronger predictor of cardiovascular risk than BMI: risk increases above 35 inches for women and 40 inches for men. Body fat percentage (use our calculator) directly measures adiposity. Waist-to-height ratio (ideal below 0.5) is simple and predictive of metabolic syndrome.
Formula
See the math
The underlying formula with variables defined, derivation shown, and a worked example with units.
Related Resources
Learn the decision before you act
Every link here is tied directly to BMI Calculator. Use the explanation, formula, examples, and benchmarks to pressure-test the calculator output from first principles.
How To Use
5 STEPSHow to Use BMI Calculator
Learn to accurately use the BMI Calculator to assess your weight status. Understand inputs, interpret results, and get practical health insights.
ReadGuide
6 MIN READHow to Calculate Your Ideal Weight
How to calculate your ideal weight using BMI, the Devine formula, body fat percentage, and waist-to-height ratio, plus why a healthy range beats one number.
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6 CRITERIABMI vs Body Fat Percentage
BMI vs body fat percentage: BMI is a weight-to-height ratio, body fat percentage measures adipose tissue directly. Pros, cons, and when each metric is most useful.
ReadFormula
3 VARIABLESBMI Formula
BMI = weight in kilograms divided by height in meters squared. Quick screening number, blind to body composition. Cutoffs are 18.5 / 25 / 30 (WHO).
ReadExamples
4 EXAMPLESBMI Examples
Explore practical BMI examples across diverse scenarios, from athletes to seniors, revealing key insights into its utility and limitations for health.
ReadStatistics
15 STATSObesity Statistics: Prevalence, Health Risks, and Trends
Evidence-based obesity statistics: US prevalence, global trends, health-cost burden, mortality risk, comorbidity rates, and treatment outcomes from CDC.
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BMI vs FFMI vs Body Fat: A 178cm/80kg Male Through Three Lenses
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Ideal weight, BMI, and FFMI engines give three target weights for the same 178cm male. Where Devine breaks, where BMI breaks, where FFMI replaces both.
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