Adult BMI Calculator
This calculator computes body mass index (BMI) from weight in kilograms and height in centimetres. It then applies the standard adult category boundaries published by the U.S. Centers for Disease Control and Prevention (CDC).
The result is intended for adults aged 20 or older. Children and teenagers require BMI-for-age percentiles based on age and sex; this tool does not perform that calculation.
Formula used
BMI is weight in kilograms divided by height in metres squared:
BMI = weight (kg) ÷ height (m)²
Because the height input is in centimetres, the calculator first divides height by 100. Both inputs must be greater than zero.
Worked example
For an adult who weighs 70 kg and is 175 cm tall:
- Convert height:
175 cm ÷ 100 = 1.75 m - Square height:
1.75² = 3.0625 m² - Divide weight by squared height:
70 ÷ 3.0625 = 22.857...
SoupCalc displays 22.86, which is in the CDC healthy-weight category for adults.
Adult BMI categories
| Category | BMI (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to less than 25 |
| Overweight | 25 to less than 30 |
| Obesity | 30 or greater |
These boundaries are screening categories, not diagnoses. A value exactly equal to 25 enters the overweight category, and a value exactly equal to 30 enters the obesity category.
How to interpret the result
BMI is a quick way to compare weight with height and can be useful for population monitoring and an initial health conversation. It does not directly measure body fat, muscle mass, fat distribution, bone density, fitness, blood pressure, blood glucose, or any disease.
People with the same BMI can have different body composition and health risks. Athletic muscularity, pregnancy, fluid retention, age-related muscle loss, limb difference, and other individual factors can make the number less representative. Health assessment may also consider medical history, physical examination, laboratory findings, waist measurements, behaviours, and personal goals.
Important boundaries
- This calculator is for adults, not for people aged 2–19 who need BMI-for-age percentiles.
- It does not diagnose malnutrition, an eating disorder, obesity-related disease, or any other condition.
- A result outside the healthy-weight category does not by itself determine what action is appropriate.
- Entering a recent measured height and weight improves reproducibility, but it does not remove BMI's underlying limitations.
If you are concerned about unexpected weight change, pregnancy, growth, nutrition, or chronic disease risk, discuss the full context with an appropriate health professional.
Sources
- CDC — Adult BMI Categories
- CDC — BMI Frequently Asked Questions
- CDC — BMI-for-Age as a Screening Measure
Editorial record
Written and manually reviewed by the SoupCalc Editorial Team. The formula, category cutoffs, and worked example were checked against the current calculator code. Last reviewed: August 10, 2026. No external medical reviewer participated. This page remains unavailable for indexing and advertising until all approved localizations pass review.