BMI Calculator

Calculate your Body Mass Index and see your healthy weight range.

Your BMI
Quick Answer

BMI = weight (kg) ÷ height² (m²). In imperial: BMI = (weight in lbs × 703) ÷ height² (inches²). A BMI of 18.5–24.9 is healthy weight, 25–29.9 is overweight, and 30 or above is obese.

What is BMI?

BMI (Body Mass Index) is a measure of body size based on height and weight. The formula is: BMI = weight (kg) / height² (m). It provides a fast, low-cost way to screen for weight categories that may lead to health problems. For adults, a BMI of 18.5-24.9 is considered a healthy weight.

BMI categories explained

The WHO and CDC use four categories: under 18.5 (underweight), 18.5-24.9 (normal/healthy weight), 25-29.9 (overweight), and 30 or above (obese). Obesity is further broken down into Class I (30-34.9), Class II (35-39.9), and Class III (40+). These thresholds are for adults aged 20 and over — children use age- and sex-specific percentile charts instead.

Limitations of BMI

BMI only uses height and weight, so it can't distinguish between muscle and fat. A muscular athlete may have a BMI in the "overweight" range while carrying very little body fat. It also doesn't account for fat distribution — abdominal (visceral) fat carries more metabolic health risk than fat stored in the hips or thighs. BMI is a screening tool, not a diagnosis.

BMI vs. body fat percentage

Body fat percentage directly measures what proportion of your body is fat, making it a more accurate picture of body composition. If your BMI puts you in the overweight range but you're physically active with significant muscle mass, check your body fat percentage for a more meaningful number. Use our Body Fat Calculator for a circumference-based estimate.

Frequently asked questions

What is a healthy BMI range?

For adults: under 18.5 is underweight, 18.5-24.9 is healthy, 25-29.9 is overweight, and 30+ is obese. These are WHO/CDC categories for adults aged 20 and over.

How is BMI calculated?

BMI = weight (kg) ÷ height² (m). In imperial: BMI = (weight in lbs ÷ height in inches²) × 703. A 5'9" person weighing 160 lbs has a BMI of 23.6.

What are the limitations of BMI?

BMI can't distinguish muscle from fat. Athletes may be flagged as overweight. It also doesn't capture where fat is distributed — abdominal fat is more metabolically harmful than fat elsewhere. BMI is a screening tool, not a diagnostic measure.

What is the difference between BMI and body fat percentage?

BMI only uses height and weight. Body fat percentage directly measures the proportion of fat in your body. A muscular person may have a high BMI but a healthy body fat percentage. Use a body fat calculator for a more accurate picture of body composition.

Does BMI apply to all adults?

Standard BMI categories apply to adults 20 and over. Children use age- and sex-specific percentile charts. The standard categories may also be less accurate for adults 65+ and some ethnic groups.