What is a healthy BMI range?

A healthy BMI ranges from 18.5 to 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is obese.

Is BMI accurate for athletes?

BMI may not be accurate for athletes or muscular individuals as it doesn't distinguish between muscle and fat mass. Athletes may have a high BMI but low body fat.

How often should I check my BMI?

It's recommended to check your BMI monthly if you're actively working on weight management, or at least annually as part of regular health check-ups.

BMI Calculator

Body mass index (BMI) is a screening ratio that compares body weight with height.

BMI Calculator Tool

Enter your values in the calculator above, then use the explanations below to understand the result, check assumptions, and compare scenarios.

About this calculator

Body mass index (BMI) is a screening ratio that compares body weight with height. It is widely used because it is fast, inexpensive, and useful for population-level risk assessment, but it does not directly measure body fat, muscle mass, bone density, or fat distribution. The calculator applies the standard adult formula and places the result in commonly used BMI ranges. Treat the number as one health indicator rather than a diagnosis, especially for athletes, older adults, pregnant people, and anyone whose body composition differs substantially from the population average.

For metric inputs, BMI = weight in kilograms ÷ height in meters². For U.S. customary inputs, BMI = 703 × weight in pounds ÷ height in inches². Adult screening ranges commonly classify BMI below 18.5 as underweight, 18.5–24.9 as healthy weight, 25.0–29.9 as overweight, and 30.0 or higher as obesity. Pediatric BMI is interpreted differently using age- and sex-specific percentiles and should not use adult categories.

Read BMI together with waist circumference, blood pressure, laboratory results, medical history, activity level, and body composition. A value near a category boundary should not be treated as a sharp change in health status. Higher BMI can reflect either excess body fat or greater lean mass, while a normal BMI can still coexist with high abdominal fat or metabolic risk.

Worked examples

Metric BMI example

A person weighs 78 kg and is 1.75 m tall.

Square the height: 1.75² = 3.0625
Divide weight by squared height: 78 ÷ 3.0625
BMI ≈ 25.47

Result: The calculated BMI is approximately 25.5, which falls just inside the adult overweight screening range.

U.S. customary BMI example

A person weighs 170 lb and is 5 ft 10 in tall.

Convert height to inches: 5 × 12 + 10 = 70 in
Square the height: 70² = 4,900
BMI = 703 × 170 ÷ 4,900 ≈ 24.39

Result: The calculated BMI is approximately 24.4, within the adult healthy-weight screening range.

Practical tips

Measure height without shoes and weight with consistent clothing conditions.
Use the same unit system throughout the calculation.
Track trends over time rather than reacting to a single measurement.
Consider waist circumference and other clinical indicators alongside BMI.
Use pediatric growth charts rather than adult BMI categories for children and teenagers.

Common mistakes

Entering feet and inches as a decimal, such as 5.10 ft, instead of converting the full height correctly.
Using adult BMI categories for children or adolescents.
Treating BMI as a direct body-fat percentage.
Assuming a normal BMI guarantees low cardiovascular or metabolic risk.
Ignoring muscularity, pregnancy, aging, edema, or other factors that affect interpretation.

Key terms

BMI: Body mass index, a screening ratio of weight to height squared.
Waist circumference: A measurement used to estimate abdominal fat distribution and related health risk.
Body composition: The proportions of fat, muscle, bone, and other tissues in the body.
Percentile: A comparison with an age- and sex-specific reference population, used for pediatric BMI.

Frequently asked questions

Is BMI the same as body-fat percentage?: No. BMI is a height-to-weight ratio. It does not distinguish fat mass from muscle, bone, or body water.
What is considered a healthy adult BMI?: The commonly used adult screening range is 18.5 through 24.9, although individual health assessment requires more context than BMI alone.
Can athletes have a high BMI without excess body fat?: Yes. Greater muscle mass can raise body weight and BMI even when body-fat levels are low.
Should children use this calculator?: Children and teenagers require age- and sex-specific BMI percentiles. Adult ranges should not be used for pediatric interpretation.
When should I discuss BMI with a clinician?: Discuss it when you have concerns about weight change, nutrition, metabolic risk, pregnancy, medications, or medical conditions. A clinician can interpret BMI with other health data.