BMI Calculator
Body Mass Index (BMI) is a simple measure using height and weight to estimate body fat. While not perfect, it's a useful screening tool for weight categories. Enter your measurements to calculate your BMI.
Reviewed by the SparkCalc editorial team · May 2026
How to use this calculator
- Choose your units — metric (kg and cm) or imperial (pounds and feet/inches).
- Enter your height and weight. The calculator uses these to compute your BMI instantly.
- Read your BMI value and the category it falls into (underweight, healthy weight, overweight, or obesity).
- Use the result as a starting point for a conversation with a healthcare professional, not as a diagnosis.
How We Calculate This
BMI is calculated as weight in kilograms divided by height in meters squared. For imperial units: (weight in lbs × 703) / (height in inches)². Categories follow CDC guidelines.
Methodology last reviewed: May 2026. How SparkCalc works
Sources: CDC – Body Mass Index (BMI)
How BMI is calculated
BMI uses one simple formula: weight in kilograms divided by the square of your height in metres (kg/m²). In imperial units, the equivalent is weight in pounds divided by height in inches squared, multiplied by 703. Because it needs only height and weight, BMI is quick, free, and consistent — which is why doctors and health agencies use it as a first-pass screening tool across large populations.
What BMI does and doesn't tell you
BMI is a screening tool, not a measure of health or body fat. It cannot tell the difference between muscle and fat, so athletes and very muscular people are often classified as "overweight" despite low body fat. It also doesn't account for where fat is stored, age, sex, or ethnicity, all of which affect health risk. Use BMI as one signal among several. Waist circumference, blood pressure, blood sugar, activity level, and a clinician's assessment give a far fuller picture than BMI alone.
BMI for children and teenagers
For anyone under 20, adult BMI categories don't apply. Children's healthy ranges change constantly with age and differ by sex, so their BMI is interpreted as a percentile against growth charts rather than a fixed cut-off. If you're checking a child's weight status, use a child-specific BMI-for-age or growth-percentile tool instead.
Key terms
- BMI (Body Mass Index)
- A number calculated from your weight and height (weight in kilograms divided by height in metres squared). It estimates whether your weight is in a healthy range for your height.
- Healthy weight range
- For adults, a BMI of 18.5 to 24.9 is generally considered healthy. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classed as obesity.
- Body composition
- The proportion of fat, muscle, and bone in your body. BMI does not measure this directly, which is why very muscular people can have a high BMI without excess fat.
Frequently Asked Questions
What is a healthy BMI?
A BMI between 18.5 and 24.9 is considered normal weight. Below 18.5 is underweight, 25-29.9 is overweight, and 30+ is obese.
Is BMI accurate?
BMI is a useful screening tool but has limitations. It doesn't account for muscle mass, bone density, age, or fat distribution. Athletes may have high BMI but low body fat.
Should I use BMI as my health measure?
BMI is one of many health indicators. Waist circumference, body fat percentage, blood pressure, cholesterol, and blood sugar are also important. Consult a healthcare provider for a complete assessment.
How is BMI calculated?
BMI = weight (kg) / height (m)². In imperial units: BMI = (weight in pounds × 703) / (height in inches)².
Related Calculators
You might also find these calculators helpful: Body Fat Calculator, and Calorie Calculator.
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This calculator provides estimates for educational purposes only. Results vary based on individual factors. Consult a healthcare professional for personalized advice.
References