How to Use This Calculator
- BMI ??enter height and weight to get Body Mass Index and the WHO category.
- Healthy Range ??given a height, returns the weight range corresponding to BMI 18.5??4.9.
- Body Fat ??uses the US Navy circumference method, validated against hydrostatic weighing for general adults.[1]
- Ideal Weight ??shows four classic ideal-weight formulas side by side.
BMI Formula
Body Mass Index, introduced by Adolphe Quetelet in the 19th century and popularized by Ancel Keys in 1972, is weight divided by height squared:[2]
BMI was designed as a population-level metric. It works reasonably well for sedentary adults but systematically misclassifies muscular individuals (athletes can appear "overweight") and underestimates body fat in older adults losing muscle mass.
WHO Categories
The World Health Organization classifies adult BMI into the following ranges:[3]
- Under 18.5 ??Underweight
- 18.5 ??24.9 ??Normal weight
- 25.0 ??29.9 ??Overweight
- 30.0 ??34.9 ??Obese Class I
- 35.0 ??39.9 ??Obese Class II
- 40.0 + ??Obese Class III
Asian populations have higher cardiometabolic risk at lower BMIs. Several Asian health authorities recommend cutoffs of 23 (overweight) and 27.5 (obese) for screening purposes.
BMI for Children and Teens
For people under 20, BMI is interpreted with age- and sex-specific percentiles rather than fixed cutoffs. The CDC growth charts are the standard reference in the United States.[4] This calculator's BMI tab reports the raw number for any age, but the WHO category labels apply only to adults.
US Navy Body Fat Method
The US Navy formula estimates body fat from circumference measurements and height. It was developed and validated against hydrostatic weighing for service-member screening:[1]
Typical accuracy is within 짹3?? percentage points compared to gold-standard methods. Measurements should be taken on bare skin at the natural waist (just above the navel for men, narrowest point for women) with the tape level and snug but not compressing the skin.
Ideal-Weight Formulas
Several formulas estimate "ideal body weight" (IBW) as a function of height and sex. They were originally developed for medication dosing in clinical settings, not as fitness targets. All take height in inches above 5 ft (60 in):
- Devine (1974) ??Male: 50 kg + 2.3 kg 횞 (in over 60). Female: 45.5 kg + 2.3 kg 횞 (in over 60).
- Robinson (1983) ??Male: 52 + 1.9 횞 (in over 60). Female: 49 + 1.7 횞 (in over 60).
- Miller (1983) ??Male: 56.2 + 1.41 횞 (in over 60). Female: 53.1 + 1.36 횞 (in over 60).
- Hamwi (1964) ??Male: 48 kg + 2.7 kg 횞 (in over 60). Female: 45.5 kg + 2.2 kg 횞 (in over 60).
Real-world healthy weight is a range, not a single number. The Healthy Range tab ??derived from BMI bounds ??is a more inclusive way to look at it.
Frequently Asked Questions
Is BMI accurate for athletes?
Often no. A muscular athlete can have a BMI in the "overweight" range while having low body fat. The Body Fat tab is a better tool in this case.
What about kids?
Use age- and sex-specific percentiles (CDC or WHO growth charts), not the adult category labels.
Does ethnicity matter?
Yes. Cardiometabolic risk at a given BMI varies between populations. Several health authorities recommend lower BMI thresholds for South Asian, East Asian, and some other populations.
References
- [1] Hodgdon J.A. & Beckett M.B. (1984). Naval Health Research Center ??Body composition equations using anthropometric measurements.
- [2] Wikipedia, "Body mass index" (CC BY-SA 4.0). en.wikipedia.org/wiki/Body_mass_index
- [3] World Health Organization ??Obesity and overweight. who.int/news-room/fact-sheets/detail/obesity-and-overweight
- [4] U.S. Centers for Disease Control and Prevention ??BMI for Children and Teens. cdc.gov
Educational content on this page is original prose written for MODOO. Material referenced from Wikipedia is used under the CC BY-SA 4.0 license.