BMI calculator
BMI is weight divided by height squared—one number that puts you in a band (underweight, normal, overweight, obese). We use WHO’s cutoffs and we’re clear about what the number does and doesn’t tell you.
API example
Same result via GET request (use current inputs above):
curl -s "https://howdeedo.com/api/calc/bmi?weight=70&weightUnit=kg&heightUnit=m&height=1.75"fetch("https://howdeedo.com/api/calc/bmi?weight=70&weightUnit=kg&heightUnit=m&height=1.75").then(r => r.json())Good to know
BMI doesn't measure health—it screens for risk. A bodybuilder and a sedentary person can have the same BMI, but vastly different health profiles. BMI correlates with health risks at the population level but tells you nothing about muscle mass, body fat percentage, or fitness. It's a screening tool, not a diagnosis. If your BMI is high but you're active and strong, your doctor isn't worried.
The cutoffs are guidelines, not laws. WHO defines 18.5–24.9 as "normal," but that's a 37-pound range for a 5'9" person (125–168 lbs). Being at 25.1 doesn't make you unhealthy; being at 24.9 doesn't make you healthy. The categories are statistical bands for population-level public health, not personal health verdicts.
BMI doesn't adjust for age or sex (on purpose). Older adults tend to lose muscle and gain fat at the same BMI. Women naturally have higher body fat percentages than men at the same BMI. WHO uses one formula for simplicity and comparability across populations. Age- and sex-specific tools exist (like child BMI percentiles), but adult BMI deliberately ignores those factors to stay simple.
Methodology
bmi-quetelet — BMI = weight (kg) / height (m)². Categories vary by population standard: WHO (global), Asian (lower cutoffs), Elderly (higher healthy range).
Assumptions
- Formula applies to adults 18 and over; not adjusted for age or sex.
- Height and weight are measured in standard units.
- WHO categories: <18.5 Underweight, 18.5–24.9 Normal, 25–29.9 Overweight, ≥30 Obese.
- Asian categories: <18.5 Underweight, 18.5–22.9 Normal, 23–27.4 Overweight, ≥27.5 Obese.
- Elderly (65+) categories: <22 Underweight, 22–26.9 Normal, 27–29.9 Overweight, ≥30 Obese.
- BMI Prime is the ratio of BMI to the upper limit of normal (25 for WHO, 23 for Asian, 27 for elderly).
Calculation version: 0.1.0
References
Disclaimers & sources
BMI is for general reference only. It is not medical advice. For health decisions, consult a healthcare provider.