Assumes: Standard BMI formula (not adjusted for age or ethnicity)WHO classification thresholdsDoes not account for muscle mass vs fat
WHO 8-tier classification, BMI Prime, Ponderal Index, body fat estimation, health risk assessment, TDEE, ideal weight comparison, and waist-to-height ratio.
Normal
Within limit
You’re in the healthy range
Daily at rest
BMI = (Weight × 703) ÷ Height²
BMI = (170 × 703) ÷ 70² = 24.4
Your position on the Body Mass Index scale
Your BMI falls within the normal range (18.5–24.9), which is associated with the lowest health risks. Maintain a balanced diet and regular physical activity.
Daily Calorie Needs
Personalized TDEE & calorie goals for your activity level
Body Composition
Body fat % + waist-to-height ratio analysis
Ideal Weight Comparison
Compare your weight across 4 medical formulas
Upgrade to PRO to unlock TDEE, body composition, and multi-formula ideal weight comparisons.
Source: CDC NHANES 2023
Body Mass Index (BMI) is a simple screening measure calculated from your height and weight. A BMI between 18.5 and 24.9 is generally considered healthy. While BMI does not directly measure body fat, it correlates with more precise methods and is widely used by healthcare providers.
BMI Prime is the ratio of your BMI to the upper limit of normal (25). A value of 1.0 means you are at the threshold. Below 1.0 is within normal range; above 1.0 indicates overweight. It provides a quick, intuitive way to see how far you are from the healthy limit.
The Ponderal Index (PI = mass/height³) is an alternative to BMI that better accounts for very tall or very short individuals. A normal PI range is approximately 11–15 kg/m³. Unlike BMI, it scales proportionally with height.
The WHO uses an 8-tier system: Severe Thinness (<16), Moderate Thinness (16–17), Mild Thinness (17–18.5), Normal (18.5–25), Overweight (25–30), Obese Class I (30–35), Class II (35–40), and Class III (40+).
BMI does not distinguish between muscle mass and fat. Athletes or highly muscular individuals may have a high BMI while being healthy. Age, gender, ethnicity, and body composition all affect what a healthy weight looks like.
Waist-to-height ratio (WHtR) is a simple measure of central obesity. Keep your waist circumference to less than half your height (ratio < 0.5). It may be a better predictor of cardiovascular risk than BMI alone.
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Free BMI calculator with WHO 8-tier classification, BMI Prime, Ponderal Index, body surface area, health risk assessment, body fat estimation, waist-to-height ratio, TDEE, and ideal weight comparison.
BMI = weight (kg) / height (m)². For US units: BMI = weight (lbs) × 703 / height (inches)². The calculator shows the formula with your actual numbers plugged in.
The WHO uses 8 tiers: Severe Thinness (<16), Moderate Thinness (16–17), Mild Thinness (17–18.5), Normal (18.5–25), Overweight (25–30), Obese Class I (30–35), Class II (35–40), and Class III (40+). This calculator uses the full 8-tier system.
BMI Prime is your BMI divided by 25 (the upper normal limit). A value of 1.0 means you are at the threshold. Below 1.0 is normal; above 1.0 indicates overweight. For example, a BMI of 27.5 gives a BMI Prime of 1.10 (10% over the limit).
The Ponderal Index (PI) equals mass divided by height cubed (kg/m³). Unlike BMI which uses height squared, PI scales better for very tall or very short people. Normal range is approximately 11–15 kg/m³.
BMI is a useful screening tool but has limitations. It does not distinguish muscle from fat, so athletes may show high BMI while being healthy. For a fuller picture, consider body fat percentage, waist-to-height ratio, and overall fitness alongside BMI.
Waist-to-height ratio (WHtR) measures central obesity. Keep your waist circumference below half your height (ratio < 0.5). Research suggests WHtR may be a better predictor of cardiovascular risk than BMI alone.
Overweight and obesity increase the risk of type 2 diabetes, heart disease, hypertension, stroke, sleep apnea, osteoarthritis, fatty liver disease, and certain cancers. Being underweight also carries risks including malnutrition, osteoporosis, and weakened immunity.
BSA estimates the total surface area of your body using the DuBois formula. It is used in medical settings for drug dosing, burn assessment, and kidney function calculations. Average adult BSA is approximately 1.7–1.9 m².
Checking your BMI once every few months is sufficient for most adults. More frequent monitoring is useful during active weight management programs or after significant lifestyle changes. Remember that short-term fluctuations in weight are normal, so focus on long-term trends rather than daily changes.
