Body composition
BMI Calculator
Your body mass index from weight and height, the CDC adult category it falls in, and the healthy-weight range for your height.
Result
Where your BMI sits
Your BMI against the CDC adult categories.
Prefer to look it up? The adult BMI chart by height and weight lists every BMI from 4′10″ to 6′4″ and 100 to 250 lb, or 150 to 195 cm and 45 to 120 kg, shaded by CDC category.
What does the BMI Calculator calculate, and which formula does it use?
The BMI Calculator divides weight in kilograms by height in metres squared and places the result in CDC's adult categories: underweight below 18.5, healthy 18.5 to under 25, overweight 25 to under 30, obesity 30 or more. The same categories apply to adult women and men; for ages 2 to 19, BMI is read as a percentile for age and sex instead.
Last updated .
How to use it
- Pick Metric or US units, then enter weight and height. Height matters most: a 1-inch (2.5 cm) error moves BMI by about 0.6 to 0.7 points at average height.
- Read your BMI and CDC category: underweight below 18.5, healthy weight 18.5 to under 25, overweight 25 to under 30, obesity 30 or more (class 1, 2 or 3). The categories screen populations; they do not diagnose an individual.
- Check the healthy-weight range for your height: the weights that put an adult of your height at BMI 18.5 up to 25.
- If you resistance train regularly, BMI can overstate body fat: two 200 lb people of the same height, one at 10% and one at 28% body fat, have the same BMI. The Body Fat Percentage Calculator measures what BMI only infers.
- Add a waist measurement for context: cardiovascular risk rises above 35 inches (88 cm) for women and 40 inches (102 cm) for 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, so BMI can label a lean, muscular lifter overweight and miss excess fat in someone of normal weight. A body fat estimate measures what BMI only guesses at.
What are the BMI ranges and what do they mean?
CDC's adult categories: underweight below 18.5; healthy weight 18.5 to under 25; overweight 25 to under 30; obesity 30 or more, split into class 1 (30 to under 35), class 2 (35 to under 40) and class 3 (40 or more). They apply to adults 20 and older and were built to screen populations, not to diagnose an individual. The adult BMI chart at /reference/bmi-chart-by-height-and-weight/ shows every band by height and weight.
Is BMI different for women and men?
No. For adults 20 and older, CDC places a BMI in the same category regardless of age, sex, or race, so women and men of the same height and weight get the same reading here. What differs is what the number is made of: BMI counts muscle and fat alike. For ages 2 to 19, BMI is read as a percentile for age and sex instead, so this calculator is for adults.
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.
The formula, worked through
- Formula BMI 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).
- Formula Ideal Weight Formula (Devine 1974)
Ideal weight formula from the Devine 1974 equation: men 50 + 2.3 kg per inch over 60, women 45.5 + 2.3, plus Robinson, Miller and Hamwi variants.
- Formula Waist-to-Hip Ratio Formula
Computes waist-to-hip ratio as waist circumference divided by hip circumference; WHO cardiometabolic risk cutoffs are 0.90 for men and 0.85 for women.
Related calculators
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Estimate body fat percentage using the U.S. Navy circumference method.
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- Nutrition Macro Calculator
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- Planning Calorie Deficit Calculator
Estimate required daily calorie deficit for a target timeline and bodyweight change.
Background on the BMI Calculator
- Guide How 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.
- Comparison BMI 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.
- Examples BMI Examples
Explore practical BMI examples across diverse scenarios, from athletes to seniors, revealing key insights into its utility and limitations for health.
- Statistics Obesity 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.
- Learn What Is BMI? Simply Explained
Understand BMI (Body Mass Index): its definition, how it's calculated using height and weight, what your score means, and why it's a key health indicator.
Articles
- 11 min read TDEE Formulas Compared: Mifflin vs Harris vs Katch
TDEE formulas compared: Mifflin-St Jeor, Harris-Benedict, Katch-McArdle, WHO/FAO. Population, error bands, and when each estimator is appropriate.
- 7 min read BMI vs FFMI vs Body Fat: A 178cm/80kg Male Through Three Lenses
Run BMI, FFMI, and Navy body-fat on the same 178cm/80kg male. Where the BMI overweight flag clashes with FFMI 22, and what to actually believe.
- 7 min read Ideal Weight vs BMI vs FFMI for a 178cm Male: Three Failure Modes
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.
By goal
Use it from code
The same calculation as a JavaScript module you can import. It runs where you import it, with no request, key or rate limit.
import { compute } from "https://aifithub.io/engines/bmi-calculator.js";Input and output contract, TypeScript types and the guide for agents.