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?
On average it carries a modestly higher risk. In a meta-analysis of 239 studies, among never-smokers without chronic disease, all-cause mortality was lowest at BMI 20-25 and about 7% higher at 25-27.5 (Di Angelantonio 2016). For an individual, waist size, blood pressure, blood glucose and lipids say more 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 same numbers as a table
- Reference BMI chart by height and weight for adults
Computed by this calculator's engine across common inputs, to cite or download as CSV.
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Background on the BMI Calculator
- Statistics Obesity Statistics: Prevalence, Health Risks, and Trends
Obesity statistics: US prevalence from CDC data, global trends, health costs, mortality risk and treatment outcomes, each figure with its source.
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.
By goal
Use it from an agent or code
Any agent can run this calculator by URL: put the inputs in the query string and get JSON back, with the inputs that used defaults and a line to cite (add format=md for markdown). MCP clients reach it through https://aifithub.io/mcp.
https://aifithub.io/api/run/bmi-calculator?weight_kg=75&height_cm=175
In code, import the same module; it runs where you import it, with no request or key.
import { compute } from "https://aifithub.io/engines/bmi-calculator.js";Input and output contract, TypeScript types and the guide for agents.