| BMI Formula | Weight (kg) ÷ Height (m²) (World Health Organization) |
| WHO 'Normal Weight' BMI Range | 18.5 – 24.9 (World Health Organization) |
| Elevated Waist Circumference (Men) | Greater than 40 in (102 cm) (National Institutes of Health) |
| Elevated Waist Circumference (Women) | Greater than 35 in (88 cm) (National Institutes of Health) |
| WHtR Reference Threshold | Below 0.5 (Emerging research; not yet universal clinical standard) |
| Most Accurate Body Fat Method | DEXA (dual-energy X-ray absorptiometry) (General clinical consensus) |
Why Multiple Metrics Matter
No single number fully describes a person's health or body composition. Body weight on a scale reflects bones, water, muscle, and organ mass alongside fat — as explored in our article what your body weight actually measures. That's why clinicians and researchers use several complementary metrics, each designed to capture something slightly different. This reference guide defines the most common measurements, explains what each one does and does not tell you, and provides generally accepted ranges — without prescribing personal targets.
This article is for general informational purposes only and is not medical advice. Always consult a qualified healthcare professional before making decisions based on any body composition measurement.
| BMI Formula | Weight (kg) ÷ Height (m²) (World Health Organization) |
| WHO 'Normal Weight' BMI Range | 18.5 – 24.9 (World Health Organization) |
| Elevated Waist Circumference (Men) | Greater than 40 in (102 cm) (National Institutes of Health) |
| Elevated Waist Circumference (Women) | Greater than 35 in (88 cm) (National Institutes of Health) |
| WHtR Reference Threshold | Below 0.5 (Emerging research; not yet universal clinical standard) |
| Most Accurate Body Fat Method | DEXA (dual-energy X-ray absorptiometry) (General clinical consensus) |
Core Body Weight Metrics: Definitions and Ranges
Body Mass Index (BMI)
BMI is calculated by dividing weight in kilograms by height in meters squared (kg/m²). The World Health Organization defines the following adult ranges: underweight (<18.5), normal weight (18.5–24.9), overweight (25–29.9), and obesity (≥30). BMI is widely used because it requires only a scale and a tape measure, but it does not distinguish fat from muscle or account for fat distribution. For a side-by-side look at its strengths and limitations compared with other tools, see BMI, body fat percentage, and waist circumference compared.
Waist Circumference
Measured at the narrowest point of the torso (or at the navel if no natural waist is present), waist circumference is a proxy for abdominal fat, which is associated with cardiometabolic risk independent of overall weight. The National Institutes of Health identifies elevated risk thresholds at >40 inches (102 cm) for men and >35 inches (88 cm) for women, though these thresholds may vary by ethnicity.
Waist-to-Hip Ratio (WHR)
WHR divides waist circumference by hip circumference. The WHO considers values above 0.90 for men and 0.85 for women to be associated with elevated abdominal obesity risk. Like waist circumference, WHR is sensitive to fat distribution rather than total fat mass.
Body Fat Percentage
This metric represents the proportion of total body weight attributable to fat tissue. Methods of measurement range from dual-energy X-ray absorptiometry (DEXA) — considered highly accurate — to bioelectrical impedance analysis (BIA), skinfold calipers, and underwater weighing. Healthy ranges differ by sex and age; broadly, essential fat is approximately 2–5% in men and 10–13% in women, with fitness and health ranges extending well above these floors. Each method carries its own margin of error, so results are most useful when tracked consistently with the same tool.
Waist-to-Height Ratio (WHtR)
An emerging metric, WHtR divides waist circumference by height. Some research suggests that keeping WHtR below 0.5 is associated with lower cardiometabolic risk across diverse populations, though clinical adoption is still growing.
BMI (Body Mass Index)
A ratio of weight to height squared (kg/m²) used to broadly categorize body weight. It is a population-level screening tool and does not directly measure body fat or account for individual variation in muscle mass.
Waist Circumference
A tape-measure assessment of abdominal girth used as a proxy for visceral (abdominal) fat. Higher values are associated with increased cardiometabolic risk independent of BMI.
Waist-to-Hip Ratio (WHR)
Waist circumference divided by hip circumference. It reflects the distribution of body fat and is used as an indicator of central adiposity risk.
Body Fat Percentage
The fraction of total body mass composed of fat tissue, expressed as a percentage. It is measured by methods such as DEXA, bioelectrical impedance, or skinfold calipers, each with differing accuracy levels.
Visceral Fat
Fat stored deep within the abdominal cavity, surrounding internal organs. Research associates elevated visceral fat with higher risk of metabolic conditions such as type 2 diabetes and cardiovascular disease.
DEXA (Dual-Energy X-ray Absorptiometry)
An imaging-based technique considered among the most accurate methods for measuring body composition, including bone density, lean mass, and fat mass.
Waist-to-Height Ratio (WHtR)
Waist circumference divided by height, used as an emerging indicator of abdominal obesity and cardiometabolic risk. A ratio below 0.5 is often cited in research as a general reference point.
Bioelectrical Impedance Analysis (BIA)
A body composition method that sends a small electrical current through the body to estimate fat and lean mass based on how tissues conduct electricity. Results can vary with hydration level.
Putting the Numbers in Context
Metrics are tools, not verdicts. Each measurement reflects a specific aspect of body composition and carries its own assumptions and limitations — a point examined in depth in common misconceptions about weight and health. For example, a highly muscular person may register a BMI in the "overweight" range while carrying very low body fat. Conversely, someone with a "normal" BMI may carry a high proportion of visceral fat that a waist circumference measurement would flag.
Body composition also interacts closely with nutrition and physical activity. Understanding your energy and macronutrient intake can complement these metrics — see our macronutrient quick-reference guide for a clear breakdown of calorie density and food sources. Interpreting any of these figures meaningfully — especially for clinical decisions — is a conversation best had with a healthcare provider who can consider your full health picture.