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ADULT HEALTH TOOL

BMI Calculator

Calculate your adult body mass index using kilograms and centimeters or pounds and feet/inches.

Your details

For adults age 20 or older. BMI is a screening measurement, not a diagnosis. It does not directly measure body fat.

Your BMI result

Updates automatically as you change values

Body mass index24.2Healthy weight
1018.5253040+
Standard healthy BMI range18.5–24.9
Weight corresponding to BMI 18.5–25 at your height53.5–72.3 kg

The weight interval is a mathematical BMI reference, not a personalized target.

Adult BMI categories

UnderweightBelow 18.5
Healthy weight18.5–24.9
Overweight25–29.9
Obesity30 or above

BMI may be less informative for muscular individuals and some other groups. It should be interpreted alongside other health measures. Adult thresholds are not applicable to people younger than 20; pregnancy also requires different assessment.

CALCULATOR GUIDE

Understand BMI Calculator

Explore the formula, worked examples and practical explanations behind this calculator.

What is BMI?

Body mass index (BMI) is a simple index that relates a person’s body weight to height. It can help with broad adult population screening, but it does not directly measure body fat, fitness, or overall health.

Adult BMI formula

For metric units:

BMI = weight in kg ÷ (height in metres × height in metres)

For US units, a commonly used approximate formula is:

BMI = 703 × weight in pounds ÷ (height in inches × height in inches)

Our tool converts pounds and feet/inches to kilograms and centimetres before calculation, avoiding rounding errors from the approximate constant 703.

Worked example

An adult who weighs 70 kg and is 170 cm tall has a BMI of:

70 ÷ (1.70 × 1.70) = 24.22, displayed as 24.2.

Standard BMI categories for adults

BMI Standard adult category
Below 18.5 Underweight
18.5 to below 25 Healthy weight
25 to below 30 Overweight
30 or above Obesity

These are broad categories for adults aged 20 and older. They should not be used for children or teens, for whom BMI-for-age interpretation is needed.

Why BMI has limitations

BMI cannot distinguish body fat from muscle, account for every difference in body composition, or establish a medical diagnosis. Pregnancy, age, activity, and clinical context can change how weight measurements should be interpreted.

How to use this BMI calculator

Select Metric or US units, enter your age, height and weight, and view the BMI figure and adult category. The range shown for the entered height is an arithmetic reference based on BMI thresholds, not an instruction to change weight.

If you have concerns about your weight, nutrition, growth, or a medical condition, speak to a qualified healthcare professional.

COMMON QUESTIONS

Frequently Asked Questions

Clear answers to help you understand your results.

01What is BMI?
BMI, or body mass index, is weight in kilograms divided by height in meters squared. It is a screening measure, not a diagnosis of body fat or health.
02How do I calculate BMI in kilograms and centimeters?
Convert centimeters to meters, square the height, then divide weight in kilograms by that number. For example, 70 kg at 170 cm gives about 24.2.
03How do I calculate BMI using pounds and inches?
Divide weight in pounds by height in inches squared and multiply by approximately 703. The calculator converts the US inputs into metric values for precision.
04What is considered a healthy BMI for adults?
Standard adult BMI categories classify 18.5 up to but not including 25 as healthy weight. This interval is a general reference, not an individualized health assessment.
05What does a BMI below 18.5 mean?
A BMI below 18.5 falls in the standard adult underweight category. Talk with a healthcare professional if you have concerns about weight or nutrition.
06What do BMI values of 25 and 30 indicate?
For adults, 25 to under 30 is categorized as overweight, and 30 or above falls in the obesity category. BMI by itself cannot diagnose a condition.
07Is BMI accurate for athletes?
BMI does not separate fat mass from muscle mass, so it can be misleading for people with higher muscularity. Other measurements and clinical context matter.
08Can I use this adult BMI calculator for children or teens?
No. People under age 20 need age- and sex-specific BMI-for-age charts or percentiles; adult BMI cutoffs should not be used.
09Should BMI be used during pregnancy?
BMI during pregnancy needs different clinical interpretation. Seek guidance from a qualified healthcare professional for pregnancy-related weight questions.
10What is the healthy-weight range shown by the tool?
It is the range of body weights mathematically corresponding to BMI values from 18.5 to 25 at the entered height. It is not a personalized weight goal.
11Does RapidCalc store my height or weight?
This calculator performs its arithmetic in your browser. Avoid entering information on shared devices if privacy is a concern.